Imagine an animal that is incapable of digesting a particular kind of food. Now suppose the mutations for digesting that food were to suddenly appear within the population. There still has to be a corresponding change in the animal's behavior, correct?
I mean, I don't go around thinking, "Gee, how could I get the best out of my genes to get ahead of my competition?" There seems to be a need for changing behaviour to get the benefit of the new mutations, which for me allows room for divine providence (e.g. A God) to guide evolution at the level of animal behavior at least.
Am I missing something? Does evolution by selection not require device providence etc?
The theory of evolution via selection does not require any kind of divine intervention. It proposes that mutations randomly occur within the DNA, this causes changes in the phenotype (e.g. allowing digestion of a common food source), these changes can be good or bad (beneficial or deleterious). As a result, those with "good" mutations achieve more reproductions (the fitness of those mutant allele carriers is higher) and those mutations spread through the population. You can not direct the evolution of your DNA because mutation is random, even if we artificially induce mutations, we can not direct what the mutation does to the phenotype (though we can sometimes induce specific mutations known to have certain phenotypic effects). Selection favours some phenotypes over others but can only work with the mutations it is presented with - it can not direct the evolution of animals with wheels if mutations that allow wheels to form do not occur.
From this sequence you can see the evolution of a phenotype is best explained in a most parsimonious way without the inclusion of divine intervention. It is the principles of Occam's Razor. Calling divine intervention in to this theory would add further, and unwarranted, complication to the model and we would then have to find strong evidence for the existence of a divine being, something which is still yet to happen in the eyes of most evolutionary biologists. Strong evidence has been found which suits the theory without divine intervention (including unnecessary and untestable components to a theory goes against the basic principles of science).
Selection itself, though largely involved in evolution, is not necessary for traits to evolve. The neutral theory proposed by Motoo Kimura and developed in the last few decades suggests that traits can evolve with out selection, via genetic drift. This means traits develop in populations purely due to random sampling of neutral (or near neutral) random alleles. The relative importance of Selectionist vs Neutralist theories remains hotly debated within evolutionary biology.
Explaining your imaginary scenario with a current theory of evolution: A new digestive enzyme
The scene: There is a population of 100 deer. 50 males and 50 females. There is a potential for variance in mating success and that mating success is defined solely by the strength of the male.
Selection affects a trait: Males that digest their food better grow bigger and stronger. Thus selection favours males that get the most out of their food. If the ability to digest is completely genetically determined by a single locus (for simplification lets say it is) and there is only one allelic variant (one version of the gene) in our first generation then mating success will be equal among the males.
A mutant arises: In the next generation a single male carries a mutation in that locus. It is a mutated version of the gene which makes a key digestive enzyme work more efficiently.
Selection acts: This male is 10% larger and stronger than other males, and therefore sires more offspring in the next generation than any other male. These next generation offspring (technically half if it was a single mutation in a diploid organism - the other half have the ancestral haplotype) have the mutant allele. Then those males with the mutant allele also get more of the matings and so on and so on.
The allele is then spreading through the population. It will continue until all members of the population have the same allele (fixation) or will start over if a new allele arises which is even better. That's all evolution is, no divine beings necessary.
What if the allele was neutral? If the gene for a digestive enzyme existed but was not necessary in an organisms diet it would not know it could go out and use that food source. It may not even be able to. For example, a single fruitfly carries a mutation which has no cost and allows it to digest lactose. It is unlikely to be able to utilize that allele, because dairy products are not part of it's diet and not available in the wild. The allele would only drift in the population, eventually being lost (most likely as it starts at low frequency) or becoming fixed in the population. You can see a genetic drift simulation I wrote in R here. You can set f=1 and then play around with population size, number of generations, and replicates to get a feel for this process.
Note it is worth considering the effects of pleiotropy (if an allele has a good effect on one trait but a negative effect on another - including traits in different environments) and linkage (if the good allele is close to some deleterious mutations in the DNA it will struggle to spread until it is separated by recombination).
@rg255 already did a good job answering the main thrust of your question, I will address this part: "There seems to be a huge amount of room for divine providence to guide evolution at the level of animal behavior, at least. Why then do scientists with a philosophical materialist outlook gloss over this?"
Of course there is "room", there is room in the theory of evolution to posit that small, green, tasty but mean little pixies come and push the new food down the creature's gullets, thus teaching them to use new food sources. There is room to posit that invisible, intelligent lichen from Alpha Centauri are actually using brain waves to guide the evolutionary choices of species in a global scale.
While there is clearly room to posit these theories, there is absolutely no evidence for them. The scientific community is not "glossing over" anything, it is just ignoring various (infinite in fact) theories for which we have absolutely no evidence in favor of those for which we have. This is a classic fallacy that was very nicely put to sleep by Russell's teapot argument:
Many orthodox people speak as though it were the business of sceptics to disprove received dogmas rather than of dogmatists to prove them. This is, of course, a mistake. If I were to suggest that between the Earth and Mars there is a china teapot revolving about the sun in an elliptical orbit, nobody would be able to disprove my assertion provided I were careful to add that the teapot is too small to be revealed even by our most powerful telescopes. But if I were to go on to say that, since my assertion cannot be disproved, it is intolerable presumption on the part of human reason to doubt it, I should rightly be thought to be talking nonsense. If, however, the existence of such a teapot were affirmed in ancient books, taught as the sacred truth every Sunday, and instilled into the minds of children at school, hesitation to believe in its existence would become a mark of eccentricity and entitle the doubter to the attentions of the psychiatrist in an enlightened age or of the Inquisitor in an earlier time.
If you feel that the world you observe is best explained by assuming the existence of an omniscient god who guides the evolutionary process, then that is your right. However, the fact that you believe this to be true does not make it so any more than my believing it to be false disproves it. We are not glossing anything over when we don't take that belief seriously, no more than when we don't take Russell's teapot seriously. The Christian faith, like many others, is built on the assumption that a god exists, it will never attempt to prove or disprove that assumption because such proof would be sacrilege, the entire edifice is built on faith not evidence. If we do not share that belief, why should we attempt to fit our observations into the ideological scaffold provided by someone else's belief system?
If you feel that one theory explains what you observe better than another, the onus is on you to prove it so. That is in fact the beauty of science, it is what sets it apart from most other areas of human endeavor: we change our minds when presented with compelling evidence to do so. Indeed, the history of science is littered with discarded theories. If you can come up with any decent evidence to support a theory, then that theory will (eventually) be taken seriously. Until you do, asking others to consider it based solely on the fact that you believe it to be true is hubris to say the least.
I think it pertinent to answer the question posed in the original title, although I will make passing reference to the specific argument the poster makes.
“Why is there such an argument about evolution?” This is because evolution is an example of a scientific question which one party approaches from a philosophical standpoint that asserts a particular answer, and so they will never be convinced by scientific arguments that ignore this philosophical position.
Note, that I am not saying that the arguments from those of a particular philosophical standpoint are necessarily wrong, only that its exponents will continue to argue (or try to engage people in argument) when the vast majority of scientists have come to regard the question as settled in favour of the counter-view - indeed when that view underpins their daily work.
There are other historical examples of this. Most well known is the Roman Catholic Church's refusal to accept Galileo's espousal of the Copernican view of the Solar System - even to look through his telescope to see the evidence. (I think they have thrown in the towel on that one now.) On the political left you have the promotion of Lysenkoism by the Soviets.
I would suggest that philosophical attitudes colour contemporary arguments. I suspect many 'progressives' would never accept scientific evidence that indicated one ethnic group were less intelligent than another. And it would be naïve to think the stage at which one regards a life as having been formed is independent of any religious or feminist views one may hold. There now. I've lost the friends I made in the previous paragraph.
Finally, your example of an individual acquiring the ability to digest a different food illustrates my point. You are so convinced that you are right that you have never taken the trouble to find out what the arguments for evolution actually are. It is only under circumstances that an acquired trait provides a competitive advantage that it will be selected for. Think multi-drug-resistant bacteria. You'll find much more sophisticated arguments on the various 'scientific creationist' sites on the Internet, but you would be advised to save your breath, because nobody is listening. As I said, la guerre est finie.
These are called psychosexual stages because each stage represents the fixation of libido (roughly translated as sexual drives or instincts) on a different area of the body. As a person grows physically certain areas of their body become important as sources of potential frustration (erogenous zones), pleasure or both.
--> all tension is due to the build-up of libido (sexual energy) and that all pleasure came from its discharge
+ The sexual instinct is the driving force of humanactivity. Sexual energy tends to accumulate and it must be reduced by achieving pleasure.
- the first five years of life are crucial to the formation of adult personality:
The id must be controlled in order to satisfy social demands this sets up a conflict between frustrated wishes and social norms.
--> The ego and superego develop in order to exercise this control and direct the need for gratification into socially acceptable channels. Gratification centers in different areas of the body at different stages of growth, making the conflict at each stage psychosexual
Role of conflict:
If they are highly successful in winning the battle (resolving the conflict), then most of the troops (libido) will be able to move on to the next battle (stage).
1. Oedipus Complex
In the young boy, the Oedipus complex or more correctly, conflict, arises because the boy develops sexual (pleasurable) desires for his mother. He wants to possess his mother exclusively and get rid of his father to enable him to do so.
Irrationally, the boy thinks that if his father were to find out about all this, his father would take away what he loves the most. During the phallic stage what the boy loves most is his penis. Hence the boy develops castration anxiety.
The little boy then sets out to resolve this problem by imitating, copying and joining in masculine dad-type behaviors. This is called identification, and is how the three-to-five year old boy resolves his Oedipus complex.
Briefly, the girl desires the father, but realizes that she does not have a penis. This leads to the development of penis envy and the wish to be a boy.
The girl resolves this by repressing her desire for her father and substituting the wish for a penis with the wish for a baby. The girl blames her mother for her 'castrated state,' and this creates great tension.
The girl then represses her feelings (to remove the tension) and identifies with the mother to take on the female gender role.
This is resolved through the process of identification, which involves the child adopting the characteristics of the same sex parent.
If progression from stage to stage is successful, a healthy personality has developed however, if it is not the case a fixation can appear.
FIXATION = in which impulses are repressed rather than outgrown. Fixation results from either excessive or insufficient pleasure during the respective pregenital stage. Until this fixation is not overcome a person stays attached to the corresponding stage.
REGRESSION = reversion to an earlier stage of development in the face of unacceptable thoughts or impulses.
Oral personality (I GET!):
Oral receptive personality: trusting, passive, depending on others. Preoccupied with eating/drinking and reduces tension through oral activity such as eating, drinking, smoking, biting nails
Oral agressive personality: egoistic, dominating, rageful. Verbally abusive to others.
Anal personality (I CONTROL!):
The Anal retentive personality is stingy, with a compulsive seeking of order and tidiness. The person is generally stubborn and perfectionist.
The Anal expulsive personality is an opposite of the anal retentive personality, and has a lack of self-control, being generally messy and careless.
Phallic personality (I AM A
exhibitionism, impulsiveness, extreme vanity, authority problems and rejection of appropriate gender roles.
Male: exhibitionistic, competitive, striving for success, emphasis on being masculine—macho—potent
Conflicts among these three structures, and our efforts to find balance among what each of them "desires," determines how we behave and approach the world. What balance we strike in any given situation determines how we will resolve the conflict between two overarching behavioral tendencies: our biological aggressive and pleasure-seeking drives vs. our socialized internal control over those drives.
According to Freud, the job of the ego is to balance the aggressive/pleasure-seeking drives of the id with the moral control of the superego.
already present from the moment of birth, it is completely unconscious and comprises instincts.
if your id walked past a stranger eating ice cream, it would most likely take the ice cream for itself. It doesn't know, or care, that it is rude to take something belonging to someone else it would care only that you wanted the ice cream.
consists of moral standards and ideals (e.g. what is good and evil) that a person has obtained from parents and society and that are internally accepted by the person: internal moral censorship.
concerned with social rules and morals—similar to what many people call their " conscience " or their "moral compass.
If your superego walked past the same stranger, it would not take their ice cream because it would know that that would be rude. However, if both your id and your superego were involved, and your id was strong enough to override your superego's concern, you would still take the ice cream, but afterward you would most likely feel guilt and shame over your actions.
a person's conscious beliefs about her/himself. Responsible for interaction with reality. The ego develops out of the id and it ensures that instincts are expressed in socially acceptable manner.
the ego is the rational, pragmatic part of our personality. It is less primitive than the id and is partly conscious and partly unconscious. It's what Freud considered to be the "self," and its job is to balance the demands of the id and superego in the practical context of reality
if you walked past the stranger with ice cream one more time, your ego would mediate the conflict between your id ("I want that ice cream right now") and superego ("It's wrong to take someone else's ice cream") and decide to go buy your own ice cream. While this may mean you have to wait 10 more minutes, which would frustrate your id, your ego decides to make that sacrifice as part of the compromise- satisfying your desire for ice cream while also avoiding an unpleasant social situation and potential feelings of shame.
Freud believed that the id, ego, and superego are in constant conflict and that adult personality and behavior are rooted in the results of these internal struggles throughout childhood. He believed that a person who has a strong ego has a healthy personality and that imbalances in this system can lead to neurosis (what we now think of as anxiety and depression) and unhealthy behaviors.
Intra-psychic conflict: (conflict between different drives, impulses, and motives held within various components of the mind)
The id demands immediate satisfaction of drives, while the superego threatens guilt if any pleasurable satisfaction of immoral impulses is attempted. It leads to intra-psychic conflict.
Personality is a field of constant battle among id and the superego that causes anxiety or internal conflict with oneself.
Freud argues for the existence of unconsciousness on the basis of the theory of repression:
defense mechanism in which unpleasant experiences are pushed out of consciousness.
Unconsciousness has an influence on person's behavior and experience, even if she is not aware of it.
Repressed experiences emerge in different ways: through language, dreams, bodily symptoms
We use defense mechanisms to protect ourselves from feelings of anxiety or guilt, which arise because we feel threatened, or because our id or superego becomes too demanding.
Defense mechanisms operate at an unconscious level and help ward off unpleasant feelings (i.e., anxiety) or make good things feel better for the individual.
Ego-defense mechanisms are natural and normal. When they get out of proportion (i.e., used with frequency), neuroses develop, such as anxiety states, phobias, obsessions, or hysteria.
REPRESSION: exclusion of an impulse that produces anxiety from consciousness
(e.g. constant forgetting).Repression is an unconscious mechanism employed by the ego to keep disturbing or threatening thoughts from becoming conscious. Thoughts that are often repressed are those that would result in feelings of guilt from the superego. For example, in the Oedipus complex, aggressive thoughts about the same sex parents are repressed.This is not a very successful defense in the long term since it involves forcing disturbing wishes, ideas or memories into the unconscious, where, although hidden, they will create anxiety.
PROJECTION: ascription of an unacceptable impulse one has to other person. This involves individuals attributing their own thoughts, feeling and motives to
another person. Thoughts most commonly projected onto another are the ones that would cause guilt such as aggressive and sexual fantasies or thoughts. For instance, you might hate someone, but your superego tells you that such hatred is unacceptable. You can 'solve' the problem by believing that they hate you.
REACTION FORMATION: converting of unwanted or dangerous thoughts, feelings or impulses into their opposites.This is where a person goes beyond denial and behaves in the opposite way to which he or she thinks or feels. By using the reaction formation the id is satisfied while keeping the ego in ignorance of the true motives. Conscious feelings are the opposite of the unconscious. Love - hate. Shame - disgust and moralizing are reaction formation against sexuality.Usually a reaction formation is marked by showiness and compulsiveness. For example, Freud claimed that men who are prejudice against homosexuals are making a defense against their own homosexual feelings by adopting a harsh anti-homosexual attitude which helps convince them of their heterosexuality. Other examples include: * The dutiful daughter who loves her mother is reacting to her Oedipus hatred of her mother.
* Anal fixation usually leads to meanness, but occasionally a person will react against this (unconsciously) leading to over-generosity.
DISPLACEMENT: substitution of an initial goal of an impulse with another, more acceptable or less threatening one.Displacement is the redirection of an impulse (usually aggression) onto a powerless substitute target. The target can be a person or an object that can serve as a symbolic substitute. Someone who feels uncomfortable with their sexual desire for a real person may substitute a fetish. Someone who is frustrated by his or her superiors may go home and kick the dog, beat up a family member, or engage in cross-burnings.
RATIONALIZATION: rational justification of a situation the true cause of which is irrational or unacceptable.Rationalization is the cognitive distortion of "the facts" to make an event or an impulse less threatening. We do it often enough on a fairly conscious level when we provide ourselves with excuses. But for many people, with sensitive egos, making excuses comes so easy that they never are truly aware of it. In other words, many of us are quite prepared to believe our lies.
6. SUBLIMATION: expression of the sexual and the destructive instincts into a creative and socially acceptable way.This is similar to displacement, but takes place when we manage to displace our emotions into a constructive rather than destructive activity. This might for example be artistic. Many great artists and musicians have had unhappy lives and have used the medium of art of music to express themselves. Sport is another example of putting our emotions (e.g. aggression) into something constructive.
For example, fixation at the oral stage of development may later lead to seeking oral pleasure as an adult through sucking ones thumb, pen or cigarette. Also, fixation during the anal stage may cause a person to sublimate their desire to handle faeces with an enjoyment of pottery.
Sigmund Freud believed that sublimation was a sign of maturity and civilization, allowing people to function normally in culturally acceptable ways. He defined sublimation as the process of , being "an especially conspicuous feature of cultural development it is what makes it possible for higher psychical activities, scientific, artistic or ideological, to play such an "important" part in civilized life". Wade and Travis present a similar view, stating that sublimation occurs when displacement "serves a higher cultural or socially useful purpose, as in the creation of art or inventions"
FIXATION = in which impulses are repressed rather than outgrown. Fixation results from either excessive or insufficient pleasure during the respective pre-genital stage. Until this fixation is not overcome a person stays attached to the corresponding stage.
REGRESSION = reversion to an earlier stage of development in the face of unacceptable thoughts or impulses.
1. Oral receptive personality:
trusting, passive, depending on others. Preoccupied with eating/drinking and reduces tension through oral activity such as eating, drinking, smoking, biting nails
2. Oral agressive personality:
egoistic, dominating, rageful. Verbally abusive to others.
Anal personality (I CONTROL!):
The Anal retentive personality
is stingy, with a compulsive seeking of order and tidiness. The person is generally stubborn and perfectionist.
The Anal expulsive personality
is an opposite of the anal retentive personality, and has a lack of self control, being generally messy and careless.
Phallic personality (I AM A MAN!):
exhibitionism, impulsiveness, extreme vanity, authority problems and either strong emphasis on gender or rejection of appropriate gender roles.
= objective psyche. It refers to the idea that a segment of the deepest unconscious mind is genetically inherited and is not shaped by personal experience.
According to Jung's teachings, the collective unconscious is common to all human beings and is responsible for a number of deep-seated beliefs and instincts, such as spirituality, sexual behavior, and life and death instincts.
--> Personality is formed in the relationship between the conscious and the unconscious aspects of psyche
SELF = total integrated personality
1) The Ego: complex of conscious ideas that constitutes the center of one's awareness.
2) The Persona: protective facade that satisfy demands of society (mask).
EGO INFALTION: Ego can identify itself with persona (mistake the formal mask for true personality).
1) Personal: contains the material derived from personal experience that is no longer (or not yet) at the level of awareness.
--> The shadow: is the primitive and unwelcome side of personality that derives from our animal ancestors. It consists of repressed (shameful) material.
The shadow is projected onto other people --> "Everything that irritates us about others can lead us to an
understanding of ourselves."
The shadow has representation in both personal and
2) COLLECTIVE UNCONSCIOUSNESS:
a storehouse of latent (inborn) predispositions to apprehend the world in particular ways (archetypes).
archetypes as universal, archaic patterns and images that derive from the collective unconscious and are the psychic counterpart of instinct. They are inherited potentials which are actualized when they enter consciousness as images or manifest in behavior on interaction with the outside world.They are autonomous and hidden forms which are transformed once they enter consciousness and are given particular expression by individuals and their cultures.
= inborn symbolically embodied universal meanings, which structure our experiences.
--> They result from the "deposits of the constantly repeated experiences of humanity" and evoke deep and sometimes unconscious responses.
--> Archetypes are represented by different symbols in all cultures, as expressed through literature, art, and dreams.
Different conceptions of welfare may change how animals are considered within a given normative theory – for example, bodily health and integrity might be considered objective goods in animals because of their intrinsic value, or instrumental toward other ends such as the reduction of unnecessary suffering or frustration of preferences (Nussbaum 2006, pp. 394–395). The aim of this paper is not to discriminate between these positions, so we assume that general markers of good and bad welfare are morally important.
Exactly which animals are considered sentient and for what reasons we shall address in a later section.
Cognitive ethology is sometimes mistaken for the pre-existing field of comparative animal psychology given their shared objectives in understanding the contents of animal minds. Major differences between the two relate to their conceptual orientations cognitive ethologists tend to assume the presence of consciousness in their account of animal cognition, while it is common for comparative psychologists to limit their discussion of mentalistic events. Other differences include experimental variation, research methodology, and limitations that scientists working in these fields might expect to encounter (Vauclair 1997, pp. 36–38, Allen and Bekoff 2007, p. 309).
Associated with the positivist view that the inclusion of non-epistemic values threatens ‘good science’ by increasing inductive risk (the risk of error in accepting or rejecting scientific hypotheses), expressed by Hempel and many others (Douglas2000, p. 561).
e.g., large farm mammals are generally given much greater priority than other animal groups in the discussion of our ethical obligations toward animals (Walker et al. 2014, p. 86). Note, however, that in recent years farmed fish have increasingly been studied with reference to welfare concepts (Lund et al. 2007, Walker et al. 2014, p. 90).
Held in addition to the common intuition that doing harm is ethically worse than allowing harm to occur.
The term ‘balance’ is often used as a metaphor in fields such as population ecology to describe the concept of equilibrium. However, its use has been criticised for being restrictive, value laden, and a general hindrance to understanding relations between natural processes (Sterelny and Griffiths 1999, p. 266, Cuddington 2001).
Examples include (Mason and Littin 2003 Littin et al., 2004 Bruce Lauber et al. 2007 Riley et al., 2007 Mafbnz 2010 Harrop 2011 Harrington et al., 2013 Ramp et al., 2016 Dubois et al., 2017).
Parallels between these two movements have increased more rapidly in recent years as the environmental impacts of industrial animal agriculture have become more apparent.
Both fields do, of course, overlap in their practice, but it is generally the case that conservation science deals with populations of animals in nature while welfare science deals domestic or human-affiliated animals.
Examples include (Faria 2016b Horta2010b, 2010c, 2010d, 2013, 2015, 2018 Johannsen 2016, 2017 Keulartz 2016 McMahan 2015 Moen 2016 Palmer 2019 Tomasik 2015 Torres 2015).
‘Good’ defined by the values held by participants in the movement.
Examples include (Clark 1979 Cowen 2003 Everett 2001 Fink 2005 Gould 1982 Hadley 2006 McMahan 2010 Næss 1991 Ng 1995 Sapontzis 1984 Simmons 2009).
See (Lord Tennyson, 1850, Darwin 1860, Salt 1894, Dunham 2008, p. 119, Mill 2008, Murray 2008, p. 2 Schopenhaur 2010, p. 432).
E.g., Peter Singer’s argument from bad consequences (that he later rejects) (Singer, 2015, p. 326, 2016), Tom Regan’s appeal to competence (Regan 2004, pp. 357 & 361), Sue Donaldson and Will Kymlicka’s ‘flourishing’ argument applied to sovereign wild animal communities (Donaldson and Kymlicka 2011, pp. 165–167), and Rosalind Hursthouse’s appeal to the virtue of respectful love (Hursthouse 2011, p. 133).
In addition to other circumstances, such as disease, which we shall discuss later in this section.
‘Survive and reproduce’ meaning ‘survive to be able to successfully reproduce in accordance with one’s evolved life history strategy’, as survival does not benefit gene transmission ipso facto.
The word ‘typically’ is used to acknowledge that there is occasionally a substantial inclusive fitness benefit to one’s continued survival post-reproduction such that the selection of traits to enhance their survival might still occur, albeit on a lesser basis.
Unless they arise contingently with other selected traits as sometimes happens.
Analysis of trade-offs between these two contrasting reproductive strategies has been termed r/K selection theory (in which r represents a species’ maximal intrinsic rate of natural growth, and K represents the carrying capacity of their local environment) (MacArthur and Wilson 1967, Pianka 1970, pp. 292–293). This method of life history classification has since received criticism for oversimplifying the study of population dynamics and producing empirically unsound predictions (Stearns 1992, p. 202, Reznick et al., 2002).
This does not imply that all other offspring members will die prematurely, for many will plausibly survive into their adulthood yet fail to successfully reproduce. Even if all offspring die prematurely a population can remain stable so long as this deficit is compensated for by other reproducing individuals within that same population.
The simple state of nonexistence is rarely considered an intrinsic source of disvalue, so we shall focus on the deprivation element of being dead.
Barring the acceptance of particular theories of consciousness, such as panpsychism, in which sentience is an intrinsic property of certain natural phenomena rather than an evolved function.
Researchers attempting to make progress on this issue include (Barr et al., 2008 Carder 2017 Diggles 2019 Eisemann et al., 1984 Elwood 2011, 2012 Klein and Barron 2016 Lockwood 1987 Puri and Faulkes 2010 Sømme 2005).
For more discussion, see (Balcombe 2016 Broom 2016 Browman et al. 2019 Brown 2015 Hurtado-Parrado 2010 Sneddon et al. 2018 Woodruff 2018).
For examples, see (Derbyshire 2016 Hart 2016 Key 2016 Rose 2002, 2007 Rose et al., 2014).
Additionally, it is not clear when sentience first emerged in the tree of life. One view, defended in Feinberg and Mallatt’s neuroevolutionary account of consciousness, posits that sentience evolved progressively throughout the phylogenetic history of vertebrates, but first appeared very early on during the Cambrian explosion (dating back some 560 or 540–520 mya) (Feinberg and Mallatt 2016, pp. 51 & 117, Godfrey-Smith 2017, p. 63).
A widespread example of such a theory supporting mutliple realizability is functionalism, which identifies mental states in terms of the functional roles they play within an organism (Putnam 1975).
E.g., even if we assume a 0.01 likelihood that terrestrial arthropods have a mental welfare, and if they do, that their moral standing is only 0.01 compared to a mammal, the case for considering their suffering might be between 10 and 10,000 times that of all extant mammals (Horta, 2010d, p.6) (Soryl, 2020, p.2). These conservative figures are intended to show the risks of ignoring the possible sentience of certain animals belonging to populous taxonomic groups, such as insects and fish.
E.g., rescuing and rehabilitating injured and sick wild animals, caring for orphaned infants who are unlikely to survive independently, or assisting animals who are victims of natural disaster. Or even small actions that assist wild animals living in urban environments, such as the regular maintenance and cleaning of bird feeders which both helps starving birds and reduces the transmission of avian disease (Jones and James Reynolds 2008, p. 268, Robb et al. 2008, p. 481).
Similar circumstances emerge in nature when there are temporarily abundant resources which cause overpopulation termed ‘Malthusian checks’.
This also involves addressing questions about animal sentience, and possibly even incorporating uncertainty as a variable affecting our conception of welfare, given our earlier discussion about insects and fish.
For examples, see (Bekoff and Pierce 2016, 2017, p. 25, Donaldson and Kymlicka 2016, Horta 2016, Johannsen 2016, Leadbeater 2016, Marino 2016, Rollin 2019).
For many reasons which due to limited space I shall not go into detail about. See (Sagoff 1984, MacClellan 2012, Paez 2015, Campbell 2018, Faria and Paez 2019) for more discussion on this issue.
Compassionate conservation is a good example of this, as well as the more recent proposal of conservation welfare. For examples, see (Beausoleil et al., 2018 Bekoff 2002 Bekoff and Elzanowski 1997 Bekoff and Jamieson 1996 Fraser 2010 Paquet and Darimont 2010 Ramp and Bekoff 2015 Wallach et al., 2015, 2018).
Alternatively, one might acknowledge the problem of WWAS and accept the position that wild animals have a negative welfare yet reject the onus of responsibility placed on humans to aid them. This position has been argued, and (in the authors view) convincingly refuted, in the following texts (Faria 2015 Palmer 2015).
Is killing yourself adaptive? That depends: An evolutionary theory about suicide
Most psychological science is the science of being and feeling like a human being, and since there is only one human being that I have or ever will have experience in being, it is not always clear to me where my career ends and my personal life begins. And this is especially salient to me right now because, like many other adult gay commentators and horrified onlookers, the raft of gay teen suicides in recent weeks has reawakened memories of my own adolescent battles with suicidal thought. There is so much I want to say about this, in fact, that I&rsquoll be breaking this column up into two separate posts, for I&rsquom reminded of the many illuminating theories and studies on suicide I&rsquove come across over the years that helped me to understand—and more importantly to overcome and to escape from—that frighteningly intoxicating desire to prematurely rid myself of a seemingly interminable hell.
If only I could have reached out and gotten hold of Tyler Clementi&rsquos shirttail before he lunged off the George Washington Bridge, or eased my fingertips between the rope and the neck of thirteen-year-old Seth Walsh before he hanged himself from a tree in his backyard, I would have pointed out to them that, one day, they will find beauty even in this fleeting despair. I would tell them that their sexual orientation places them in the company of some of the greatest figures and secular angels in creative history—to name just a few, Michelangelo, Caravaggio, Oscar Wilde, Andy Warhol, Leonardo da Vinci, Marcel Proust, Jean Genet, Hans Christian Anderson and Tchaikovsky. Finally, I&rsquod tell them about the scientific research and ideas that I&rsquom going to share with you, razor-sharp reasoning by bright scholars that may have pierced their suicidal cognition just enough to allow them to breathe a little more easily through those suffocating negative emotions.
In fact, a scientific understanding of suicide is useful not only for vulnerable gay teens, but for anyone ever finding themselves in conditions favoring suicide. I say &ldquofavoring suicide&rdquo because there is convincing work—all tracing back to McMaster University&rsquos Denys deCatanzaro&rsquos largely forgotten ideas from the early 1980s—indicating that human suicide is an adaptive behavioral strategy that becomes increasingly likely to occur whenever there is a perfect storm of social, ecological, developmental and biological variables factoring into the evolutionary equation. In short, deCatanzaro has posited that human brains are designed by natural selection in such a way as to encourage us to end our own lives when facing certain conditions, because this was best for our suicidal ancestors&rsquo overall genetic interests.
For good-hearted humanitarians, it may sound rather bizarre, perhaps even borderline insensitive, to hear that suicide is &ldquoadaptive.&rdquo But remember that this word means a very different thing in evolutionary terms than it does when used in clinical settings. Because natural selection operates only on phenotypes, not human values, even the darkest of human emotions may be adaptive if they motivated gene-enhancing behavioral decisions. It&rsquos not that evolution is cruel, but as a mindless mechanism it can neither care nor not care about particular individuals selection, after all, is not driven by an actual brain harboring any feelings about, well, anything at all. In no case does this sobering fact come into sharper focus than with the case of adaptive suicide. (I notice a similar reactionary confusion, incidentally, among &ldquoNew Atheists&rdquo who bleat and huff in a Dawkinsian manner whenever they hear mention of the empirically demonstrable fact that religion is adaptive, something I&rsquoll save for another day.)
Saying that suicide is adaptive may also sound odd to you from an evolutionary perspective, because on the surface it seems to fly in the face of evolution&rsquos first rule of thumb, which is to survive and reproduce. However, as William Hamilton&rsquos famous principle of inclusive fitness elucidated so clearly, it is the proportion of one&rsquos genetic material surviving in subsequent generations that matters and so if the self&rsquos survival comes at the expense of one&rsquos genetic kin being able to pass on their genes, then sacrificing one&rsquos life for a net genetic gain may have been adaptive ancestrally.
Before we get ahead of ourselves, let&rsquos first ease into the suicide-as-adaptation argument with a few nonhuman examples, which come mostly from the insect and arthropod worlds. Take male Australian redback spiders (Latrodectus hasselti), for instance, which seem content to be cannibalized by—to say the least—sexually aggressive female redback spiders during sex. Aside from putting a damper on an otherwise enjoyable act, being eaten alive while copulating would seem rather counterintuitive from an evolutionary perspective. But when biologists looked more closely at this spidery sex, they noticed that males that are cannibalized copulate longer and fertilize more eggs than males that are not cannibalized and the more cannabilistic a female redback spider is, it turns out, the more desirable she is to males, even rejecting more male suitors. Another example is bumblebees (Bombus lucorum), a species that is often parasitized by invidious little conopid flies that insert their larva in the bee&rsquos abdomen. Once infected, the bumblebee dies in about twelve days, and the parasitical flies pupate until their emergence the following summer. What&rsquos interesting about this, however, is that parasitized bumblebees essentially go off to commit suicide by abandoning their colony and spending their remaining days alone in far-away flower meadows. In doing so, these infected bumblebees are leading the flies away from nonparasitized kin, increasing inclusive fitness by protecting the colony from infestation.
What is critical to take away from these examples is that the suicidal organism is not consciously weighing the costs of its own survival against inclusive fitness gains. Redback spiders and bumblebees aren&rsquot mindfully crunching the numbers, engaging in self-sacrificial acts of heroic altruism, or waxing philosophically on their own mortality. Instead, they are just puppets on the invisible string of evolved behavioral algorithms, with neural systems responding to specific triggers. And, says evolutionary neurobiologist Denys deCatanzaro, so are suicidal human beings whose emotions sometimes get the better of them.
So let&rsquos turn our attention now to human suicide. To crystallize his position, I present deCatanzaro&rsquos &ldquomathematical model of self-preservation and self-destruction&rdquo (circa 1986):
Where &Psii = the optimal degree of self-preservation expressed by individual i (the residual capacity to promote inclusive fitness)
&rhoi = the remaining reproductive potential of i
&rhok = the remaining reproductive potential of each kinship member k
bk = a coefficient of benefit (positive values of b k ) or cost (negative values of b k ) to the reproduction of each k provided by the continued existence of i (-1 &le b &le 1)
rk = the coefficient of genetic relatedness of each k to i (sibling, parent, child = .5 grandparent, grandchild, nephew or niece, aunt or uncle = .25 first cousin = .125 etc.).
For the mathematically disinclined, this can all be translated rather straightforwardly as follows: People are most likely to commit suicide when their direct reproductive prospects are discouraging and, simultaneously, their continued existence is perceived, whether correctly or incorrectly, as reducing inclusive fitness by interfering with their genetic kin&rsquos reproduction. Importantly, deCatanzaro, as well as other independent researchers, have presented data that support this adaptive model.
In a 1995 study in Ethology and Sociobiology, for example, deCatanzaro administered a 65-item survey including questions about demographics (such as age, sex and education), number and degree of dependency of children, grandchildren, siblings and siblings&rsquo children, &ldquoperceived burdensomeness&rdquo to family, perceived significance of contributions to family and society, frequency of sexual activity, stability/intimacy/success of relations to the opposite sex, homosexuality, number of friends, loneliness, treatment by others, financial welfare and physical health, feelings of contentment, depression, and looking forward to the future. Respondents were also asked about their suicidal thoughts and behaviors—for example, whether they had ever considered suicide, whether they had ever attempted it in the past, or ever intended to do so in the future. The survey was administered to a random sample of the general Ontario public, but also to theoretically targeted groups, including elderly people from senior citizen housing centers, psychiatric inpatients from a mental hospital, male inmates incarcerated indefinitely for antisocial crimes and, finally, exclusively gay men and women.
Many fascinating—and rather sad—findings emerged from this study. For instance, the greatest levels of recent suicide ideation were in male homosexuals and the psychiatric patients, whereas the prison population showed the most previous suicide attempts. &ldquoIt gets better,&rdquo sure, but we&rsquore always at risk, and this evolutionarily informed model helps gay individuals to come to grips with that lamentable reality. But the important takeaway message is that the pattern of correlational data conformed to those predicted by deCatanzaro&rsquos evolutionary model. Although the author offers the important disclaimer that &ldquothe observational nature of this study limits strong causative inferences,&rdquo nevertheless:
One noteworthy thing to point out in such data is the meaningful developmental shift that occurs in the motivational algorithm. Whereas heterosexual activity is the best inverse predictor of suicidal thoughts among younger samples, this is largely replaced among the elderly by concerns about finances, health and especially the sense of &ldquoperceived burdensomeness&rdquo to family. A few years after this Ethology and Sociobiology report, a follow-up study in Suicide and Life-Threatening Behavior, conducted by an independent group of investigators seeking to further test deCatanzaro&rsquos model, replicated the same predicted trends.
As persuasive as I find this model, I still had a question left unanswered by deCatanzaro&rsquos basic argument, so last week I dropped him an email seeking clarification. Basically, I wanted to know how the suicidal patterns of contemporary human beings relates to those of our ancestral relatives, who presumably faced the conditions in which the adaptation originally evolved, but who in many ways lived in a very different world than our own. After all, even with guns, knives and drugs at our disposal, committing suicide is not always an easy thing to do, logistically speaking. In an article published earlier this year in Psychological Review, for instance, University of Rochester psychiatrist Kimberly Van Orden and her colleagues cite the case of a particularly tenacious suicidal woman:
Now consider the suicide methods that would have been available to our ancient relatives in a technologically sparse environment—perhaps a leap from a great height where, if one weren&rsquot successful, might have at least led to wounds sufficient enough for the person to eventually die from infection. Starvation. Exposure. Drowning. Hanging. Offering oneself to a hungry predator. Okay, so maybe there were more methods available to our ancient forebears than I realized. You see what I mean, though. Today, moving your fingertip but by a hairsbreadth is a surer route to oblivion than anything our species has ever known before gun-owners might as well have an &ldquooff&rdquo button, it&rsquos so simple now. (This is one of the many reasons that I don&rsquot own a gun—deCatanzaro&rsquos suicide algorithm is stochastic, which means that the figure it generates for a given individual is in a constant state of flux.) But deCatanzaro doesn&rsquot see technological advances as particularly problematic for his adaptationist model. Fossils of suicidal australopithecines or early Homo sapiens aren&rsquot easy to come by, of course. But, as he told me in his email response to my questions:
Evidence indicates appreciable rates of suicide throughout recorded history and in almost every culture that has been carefully studied. Suicide was apparently quite common in Greek and Roman civilizations. Anthropological studies indicate many cases in technologically primitive cultures as diverse as Amerindians, Inuit, Africans, Polynesians, Indonesians, and less developed tribes of India. One interesting old review was written by [S. R.] Steinmetz in 1894 (American Anthropologist 7:53-60). Self-hanging was one of the most prevalent methods of suicide in such cultures. There are also data from developed countries comparing suicide rates from the late 19th century through the 20th century. These data show remarkable consistency in national suicide rates over time, despite many technological changes. So, the data actually do not show a major increase in suicide in modern times, although this inference must be qualified in that there may have been shifts in biases in recording of cases.
Interestingly, the methods of suicide have changed much more than the rates. For example in Japan, hanging prevailed until 1950, after which pills and poisons became the primary method. In England and Wales, hanging and drowning were common in the late 19th century, but were progressively replaced by drugs and gassing. Motives may have been more constant than means (italics added).
I find deCatanzaro&rsquos argument that suicide is adaptive both convincing and intriguing. But I do think it begs for more follow-up research. For example, his inclusive fitness logic should apply to every single social species on earth, so why is there such an obvious gap between frequency of suicide in human beings and other animals? Each year, up to 20 million people worldwide attempt to commit suicide, with about a million of these completing the act. That&rsquos a significant minority of deaths—and near deaths—in our species. And there is reason to be suspicious that nonhuman animal models (such as parasitized bumblebees, beached whales, leaping lemmings and grieving chimpanzees) are good analogues to human suicide. In our own species, suicide usually means deliberately trying to end our psychological existence—or at least this particular psychological existence. And whereas most other accounts of &ldquoself-destruction&rdquo in the natural world seem to involve some type of interspecies predation or parasitical manipulation, human suicides are more often driven by negative interpersonal appraisals made by other members of our own species. In fact, Robert Poulin, the University of Otago zoologist who first reported on the altered behavior of those parasitized bumblebees, even urges researchers to use caution in referring to such examples as &ldquosuicide&rdquo:
I've got a hunch that suicide, like fantasy-enabled masturbation, may require recently evolved social cognitive processes that are relatively unique—in this case, painfully so—to our species. There are anecdotes aplenty, of course, but there are no confirmed cases of suicide in any nonhuman primate species. Although there are certainly instances of self-injurious behaviors, such as excessive self-grooming, these are almost always limited to sad or abnormal social environments such as biomedical laboratories and zoos. Yes, grieving young chimps have been known to starve to death from depression in the wake of their mothers&rsquo death, but there is no evidence of direct self-inflicted lethal displays in monkeys and apes. Perhaps Jane Goodall can correct me if I&rsquom wrong about this, but as far as I&rsquom aware, there are no cases in which a chimpanzee has been observed to climb the highest branch it could find—and jump.
I think part of the answer to this cross-species mystery can be found in another theoretical model of suicide, this one by Florida State University psychologist Roy Baumeister, which I&rsquove always viewed as the &ldquoproximate&rdquo level to deCatanzaro&rsquos &ldquoultimate&rdquo level of explanation for suicide. These are not alternative accounts of human suicide, but deeply complementary ones. While deCatanzaro explains suicide in terms of evolutionary dynamics, Baumeister zeros in on the specific psychological processes, the subjective lens by which a suicidal person sees the world. His model describes the engine that actively promotes the adaptive response of suicide. I should hasten to add that I don&rsquot think either of them— deCatanzaro or Baumeister—necessarily see their models as being complementary in this way. I don&rsquot even know if either is aware of the other. But this is how the two approaches have always struck me. Baumeister&rsquos 1990 Psychological Review article on the subject, titled &ldquoSuicide as Escape From Self,&rdquo is, quite honestly, one of the most shockingly insightful manuscripts I have ever read, in any research literature.
And it&rsquos that piece that I&rsquoll kick off with later this week in &ldquoPart II&rdquo on the science of suicide along with other evolutionary tidbits. I&rsquoll also discuss more current work, including some thoughts about why I believe modern schools place vulnerable adolescents, such as gay teens, at heightened risk of suicide simply by creating an artificial social environment of exclusively same-age peers, one in which specific pressure-points of ancestral conflict are bizarrely exacerbated. &ldquoIt gets better&rdquo for gay teens only because we eventually get out of that unnatural zoo that is high school.
The views expressed are those of the author(s) and are not necessarily those of Scientific American.
Does evolution by selection require that individuals consciously change behaviour in an effort to suit their genes? - Biology
The increase in relative abundance of the dark type was due to natural selection. The late eighteen hundreds was the time of England's industrial revolution. Soot from factories darkened the birch trees the moths landed on. Against a sooty background, birds could see the lighter colored moths better and ate more of them. As a result, more dark moths survived until reproductive age and left offspring. The greater number of offspring left by dark moths is what caused their increase in frequency. This is an example of natural selection.
Populations evolve, not individuals. In order to understand evolution, it is necessary to view populations as a collection of individuals, each harboring a different set of traits. A single organism is never typical of an entire population unless there is no variation within that population. Individual organisms do not evolve, they retain the same genes throughout their life. When a population is evolving, the ratio of different genetic types is changing -- each individual organism within a population does not change. For example, in the previous example, the frequency of black moths increased the moths did not turn from light to gray to dark in concert.
The process of evolution can be summarized in three sentences: Genes mutate. Individuals are selected. Populations evolve.
Thomas Malthus (1766-1834) was an English clergyman, whose writings on population growth had a strong influence on the theory of evolution by natural selection developed by Charles Darwin and Alfred Russel Wallace.
- Malthus shows that organisms produce more offspring than can survive
- populations grow faster than food supply = struggle for existence
Even when resources are plentiful, the size of a population tends to increase geometrically until the population outstrips its food supply. This led Malthus to believe that poverty, disease, and famine was a natural and inevitable phenomenon, leading to a "struggle for existence".
- Darwin proposed mechanism of natural selection based on observations in South Pacific wildlife
- uniformatarianism = evolution is a long term process
- The five components of evolution are:
- nonconstancy of species (individuals are unique)
- all organisms descent from common ancestors
- gradualness of evolution
- multiplication of species (diversity)
- natural selection
In Darwin's theory of natural selection, new variants arise continually within populations. A small percentage of these variants cause their bearers to produce more offspring than others. These variants thrive and supplant their less productive competitors. The effect of numerous instances of selection would lead to a species being modified over time.
- increased reproductive capability = natural selection (not weeding)
- survival is not only factor, sexual selection, enhanced characteristics also contribute
Natural selection can be broken down into many components, of which survival is only one. Sexual attractiveness is a very important component of selection, so much so that biologists use the term sexual selection when they talk about this subset of natural selection. Sexual selection is natural selection operating on factors that contribute to an organism's mating success.
- selection can occur in many ways, outlined above are stabilizing, disruptive, directional
- extremes are controlled by energy requirements
- unique human characteristics =
- steroscopic vision
- high mobility (upright stance)
- opposable thumbs
- developed about 20 million years ago in East Africa
The Miocene climate was warmer than that of the present day and tropical forests were much more widespread. About 12 million years ago the world began to cool which would eventually lead to the onset of the Ice Age (1 million years ago). At this time, a tree-dwelling primate developed:
Upright walking was a response to environmental changes in East Africa at the time, the rainforest was turning into steppes and grasslands due to global cooling. This reduced the apes' habitat and drove 2/3's of their species into extinction. Some primates developed arboreal lifestyles and became the gibbon lineage. Others, developed an upright stance, as a survival characteristic to see over tall grasses, and spent more time on the ground. About 3.5 million years ago, our first direct ancestor appeared, Australopithecus africanus, whose best fossil example is should below.
- IQ was not a selected trait but a byproduct of increased brain capacity due to larger body size and visual processing
This illustration compares the crania of a female gorilla, Australopithecus africanus, and Homo sapiens. The dark area at the bottom of the skull is the foramen magnum, the hole through which the spinal column passes. It has a forward position in australopithecine skulls, a strong indication that they were bipedal. Note also that both the shape of the jaw and the teeth of australopithecines are very similar to those of modern humans. Australopithecines do not have the rectangular-shaped jaw or the large canine teeth of apes.
- DNA tracing confirms Africa origin to human species
- the hominid family tree is `bush-like' with numerous hominid species existing at the same time
Our current idea of the human family tree is shown below, whose origins lie on the continent of Africa, then spread around the globe. We also know that every living human is the direct descendent of a single Homo Sapian woman who lived in Africa 150,000 years ago (i.e. Eve) based on the matching of DNA from cellular mitochondria in people around the world. Notice that our last common ancestor with apes is Australopithecus ramidus, about 5 million years ago. Also note that many species of Australopithecus and Homo are now extinct.
- Which came last?
- upright walking
- tool making
The basic premise here is that culture has some advantage for the survival of our ancestors, therefore natural selection favors genes responsible for such behavior. DNA information only passes from individual to individual, but cultural evolution is active, incorporates a lifetime of teaching and can be passed from one individual to many. Cultural evolution, with its global nature, becomes the distinguishing characteristic of humans.
An important aside is that very few of those involved in these debates dispute that the things that each points to actually happen. They acknowledge that the natural world is full of different and complex causes and phenomena. The argument is one about relative frequency&mdashwhich of the causes or phenomena is the dominant one in a statistical sense. This, whether we like it or not, is the nature of truth in this branch of science.
Darwin himself, for example, always insisted that natural selection was not the only mechanism of evolution, but rather that is was the main or dominant mechanism. In a famous passage which an exasperated Darwin added to the sixth edition of The Origin of Species in 1872, he wrote:
As my conclusions have lately been much misrepresented, and it has been stated that I attribute the modification of species exclusively to natural selection, I may be permitted to remark that in the first edition of this work, and subsequently, I placed in a most conspicuous position&mdashnamely at the close of the Introduction&mdashthe following words: ‘I am convinced that natural selection has been the main but not the exclusive means of modification.’ This has been to no avail. Great is the power of steady misrepresentation.18
With that warning in mind let me turn to perhaps the most important, pillar of Gould’s argument.
The Three Necessary and Sufficient Conditions of Natural Selection
Natural Selection is the key creative force in evolution. Natural selection, together with specific histories of populations (species) and adaptations, is responsible for the design of organisms. Most people have some idea of what Natural Selection is. However, it is easy to make conceptual errors when thinking about this important force of nature. One way to improve how we think about a concept like this is to carefully exam its formal definition.
In this post, we will do the following:
- Discuss historical and contextual aspects of the term "Natural Selection" in order to make clear exactly what it might mean (and not mean).
- Provide what I feel is the best exact set of terms to use for these "three conditions," because the words one uses are very important (there are probably some wrong ways to do it one would like to avoid).
- Discuss why the terms should be put in a certain order (for pedagogical reasons, mainly) and how they relate and don't related to each other.
When you are done reading this post you should be able to:
- Make erudite and opaque comments to creationists that will get you points with your web friends.
- Write really tricky Multiple Choice Exam Questions if you are a teacher.
- Evolve more efficiently towards your ultimate goal because you will be more in control of the Random Evolutionary Process (only kidding on this third one. )
Here are some definitions of Natural Selection I found on the web for your review:
- The differential survival and reproduction of organisms with genetic characteristics that enable them to better utilize environmental resources [source]
- Natural selection is the process in which some organisms live and reproduce and others die before reproducing. Some life forms survive and reproduce because they are better suited to environmental pressures, ensuring that their genes are perpetuated in the gene pool. [source]
- Process by which the genotypes in a population that are best adapted to the environment increase in frequency relative to less well-adapted genotypes over a number of generations. source
- The concept developed by Charles Darwin that genes which produce characteristics that are more favorable in a particular environment will be more abundant in the next generation. [source]
- the differential survival and/or reproduction of individuals within a population based on hereditary characteristics. [source]
- The process by which new species evolve when influenced by selective pressure (Martin et al, 2000). Natural selection occurs when the natural factors of environmental resistance tend to eliminate those members of a population that are least well adapted to cope and thus, in effect, select those best adapted for survival and reproduction (Nebel et al, 1998). [source]
- central thesis of the biologist Charles Darwin which suggests that within every population of living organisms there are random variations which have different survival value. Those which aid survival (or enhance reproductive capacity) are 'selected' by being genetically transmitted to succeeding generations. [source]
There are things I don't like about most of these definitions. A definition may focus on environmental conditions and thus ignore many very important other things such as developmental processes and mating. Definitions may focus on the individual's survival, etc., which works, but we may want to speak of traits as well as individuals. Some definitions use active verbs such as "ensuring that their genes are perpetuated in the gene pool." This may not be linguistically wrong but it incorporates teleological concepts, which don't need our help in creeping into our thinking (especially in the formal definition of a natural force!). There is often a direct link to Charles Darwin. This is good because it is true that this is his concept. However, a modern definition of Natural Selection needs to be Neo-Darwinian. So specifically referring in the definition to Darwin without more attention to the historical development is inadequate. Referring to Darwin's concept as a concept about genes is jarringly wrong.
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As a whole these definitions are not terrible, but they are mostly flawed for one reason or another. The definition I want to lay out here will have specific reference to the same process these definitions are about. However, there is also one very large problem with many of these definitions that is a bit more subtle than most but that is, to me, critical, that relates to the object of study. It is probably best to not assume a one-to-one correspondence between the process of Natural Selection that we are going to describe here and the concept of "adaptation." Ultimately, I would like to say that "adaptation" is the noun and "Natural Selection" is the verb in a key evolutionary process. But having said that, a useful and precise definition of Natural Selection may have to leave out processes that are nonetheless related to adaptations, both in terms of understanding the historical aspects of an adaptation and the functional aspects, but that do not fall under the process "Natural Selection" as it is best defined.
An adaptation may reach its particular form through the process of Natural Selection, but there are aspects to that form that have to do with, for instance, abiotic realities. You cannot have adaptations that involve swimming without bodies of water, for example. Our definition does not say "Oh, and there must be air, and water, and trees to climb in."
I actually want to provide TWO different (linguistically) but identical (functional) definitions of natural selection. The first is the coolest one, the simplest one, the one that makes you think. The second is a better pedagogical tool and serves better as the basis for adaptationist analysis of biological systems. The second also links better to certain historical aspects of the development of the concept.
The first definition is conceptually related to the following definition of evolution:
Change in allele frequency over time.
Which is something of an oversimplification, but an allowable one. And in this context we can define Natural Selection as:
Nonrandom elimination of alleles.
I believe that this was suggested by Ernst Mayr.
This is a cool definition because it is short, sweet, and correct. Note the very important asymmetry that this definition implies. There is no non-random generation of novel alleles. Only elimination. This jibes with selection as a creative force, but neutral processes as providing the raw material. Neutral processes lay down the sediments that become the marble, Natural Selection is the sculptor. The adaptation is the sculpture.
The second definition, and the one I really want to get to, involves the so called "three necessary and sufficient conditions" and it goes something like this:
- Variation in a trait
- Heritability of the trait
- Differential fitness conferred by the trait.
Just as important as these elements is the theoretical and logical framework in which they are placed. They are the THREE NECESSARY and SUFFICIENT conditions. Let's parse that out more.
Three . That there are three is obviously because all important things happen in threes, sevens, or tens, for unknown cosmic reasons. Be that as it may, I want to point out that "three" implies "three different" things. If two of them could have been combined, then we would have only two. But there are three.
What this implies is the following: If there is a trait that varies, then it meets the first criterion. But "No," you say, "what about hair color? If I see a bunch of people with different color hair, and I KNOW they dyed their hair to get that way, this is not trait related to selection. So it does not meet the first criterion."
But you would be wrong. Remember, there are THREE DIFFERENT criteria. The first one is variation. If you see a bunch of dogs and they have different coats because they went to a very creative groomer, or a bunch of students standing around the cafeteria with blue, red, unnaturally black, and vivid yellow hair because they all went to Target and got dye and colored their hair, then in both cases you have met the first criterion because there is variation. By saying "these traits are not inherited" you have skipped ahead and cheated.
The second criterion is usually stated as "heritability" and that is a small problem, because the term "heritability" has a specific meaning in biostats that falls apart for our present use. It is the measured variance in the genotype divided by the measured variance in the phenotype, squared. (Thus indicating something like the proportion of measured phenotypic variance that is accountable by genetic variation.) What is meant in our definition, however, is this: Is the variation in the trait conferred by genes? The dyed hair and the clipped poodle do not meat this criterion.
The third criterion is often stated as "Differential Reproductive Success" and that is simply wrong. The correct term is "Differential fitness" and it has to be differential fitness that is conferred by the trait. Why fitness instead of Reproductive Success (RS)? That is an important matter, and I will not discuss it here. For now, let's just go with it.
OK, back to the theoretical context: Necessary.
Why are these three necessary? By necessary it is meant that ALL of them have to be true or it is not Natural Selection. This is fairly obvious. If you are missing any one of these three then what you are observing may be an interesting phenomenon but it is not Natural Selection. This also speaks to the need to be Neo-Darwinian. Darwin was aware of inheritance, but lacking an understanding of the mechanism, the necessary requirement of "heritability" (remember, shorthand for "the trait is passed on by genes"), any Darwinian definition (and I've avoided using his specific words here) is not good enough.
I had said at the beginning that the ordering of the three conditions is important. This is because they interact with each other in order. Here is how.
First, you need a trait that shows variation. Second you need to show that that trait is heritable, AND that the inheritance pattern relates to that variation. Third you need to show that the variation that is heritable maps on to differential fitness. So there is a strong logic to the order, that is embedded in the functional meaning of Natural Selection and any test criteria that are set up to investigate possible cases of it.
So the ordering works both for the understanding of the concept (pedagogy) and the investigation of the phenomenon.
Sufficient. That is a really important part of the context for this definition. If these three conditions are true, then Natural Selection IS happening. There is no alternative. The force of Natural Selection is activated when these three conditions are met, no matter what.
Does this mean that the selective force will have an effect? It depends. Natural Selection is a force, but there are other forces, including other instances of Natural Selection that may be operative in a particular organism. Gravity is a force but a fly can still walk on the ceiling. The gravity is still acting on the fly, but so is another force (adhesion) that keeps it up there.
This is an important point that bears emphasis. When the Three N&S Conditions of N.S. are working, Natural Selection happens. Period. The absence of an EFFECT is due to countervailing forces (including chance, because within it's operation there are still stochastic effect).
I believe it is incorrect and counterproductive to make "Sexual Selection" distinct from and parallel to "Natural Selection." Darwin was puzzled by apparent inconsistencies, especially along the lines of exaggerated traits mostly in males, and came up with Sexual Selection as a process to explain this. Fine. But I think it is best to think of both Sexual and Artificial Selection as subsets of Natural Selection.
The term "Selection" by itself is often used interchangeably with "Darwinian Selection," but often (usually?) as not really meaning the same thing as Natural Selection. Natural Selection works between generations on reproducing organisms and their genomes. Darwinian Selection, or selection in general can work on other things, like prospective students trying to get into law school, or neurons during culling, etc.
This has been an enhanced repost from a very long time ago. You might imagine that I'm about to write a post on Falsehoods related to Natural Selection, and needed this post nearby. You'd be right!
Other posts of interest:
Also of interest: In Search of Sungudogo: A novel of adventure and mystery, which is also an alternative history of the Skeptics Movement.
Does Depression Have an Evolutionary Purpose?
I had a tough time in high school. Like many other young adolescents, I saw myself as fundamentally flawed, and felt a searing isolation. Nothing I looked forward to brought any hope. I stopped getting out of bed. I cut myself. I drafted a suicide note.
It was a terrible time that I wouldn’t wish on anyone. But in a strange way, my self-destructive behavior may have had a benefit. I eventually dropped clues about my situation, leading to an intervention that put me on a better track. I was hospitalized. It scared me straight, highlighting a pathway of suffering I no longer wanted to indulge. I went back on medication and did what it took to stay at my school.
costly signal: According to the bargaining model of suicidality, an attempt to take one’s own life is a costly, and therefore honest, signal to one’s network—characteristics shared by a peacock’s tail. ngela Nicholson/PhotoPlus Magazine via Getty Images
One in six Americans will suffer a major depressive disorder at some point in life. 1 That word—disorder—characterizes how most of us see depression. It’s a breakdown, a flaw in the system, something to be remedied and moved past.
Some psychologists, however, have argued that depression is not a dysfunction at all, but an evolved mechanism designed to achieve a particular set of benefits. I’ve certainly considered whether it’s done that for me, both in high school and later in life. If they’re right, it means that our thinking about depression needs an intervention too.
T heories about the evolutionary function of depression are numerous. 2 One of the most popular current ideas is the analytical rumination hypothesis. This idea was described most thoroughly in a long 2009 article by Paul Andrews, an evolutionary psychologist now at McMaster University, and J. Anderson Thomson, a psychiatrist at the University of Virginia Student Health Services. 3 Andrews had noted that the physical and mental symptoms of depression appeared to form an organized system. There is anhedonia, the lack of pleasure or interest in most activities. There’s an increase in rumination, the obsessing over the source of one’s pain. There’s an increase in certain types of analytical ability. And there’s an uptick in REM sleep, a time when the brain consolidates memories.
Andrews sees these symptoms as a nonrandom assortment betraying evolutionary design. After all, why would a breakdown produce so synchronized a set of responses? And that design’s function, he argues, is to pull us away from the normal pursuits of life and focus us on understanding or solving the one underlying problem that triggered the depressive episode—say, a failed relationship. If something is broken in your life, you need to bear down and mend it. In this view, the disordered and extreme thinking that accompanies depression, which can leave you feeling worthless and make you catastrophize your circumstances, is needed to punch through everyday positive illusions and focus you on your problems. In a study of 61 depressed subjects, 4 out of 5 reported at least one upside to their rumination, including self-insight, problem solving, and the prevention of future mistakes. 4
“It may be best to let depression work its miserable magic, under protective supervision.”
“Most episodes of depression end on their own—something known as spontaneous remission—and Paul may have an explanation for just how that happens,” says Steven Hollon, a professor of psychology at Vanderbilt University. Further, “cognitive behavioral and problem-solving therapies may work precisely because they tap into and accelerate—in a matter of weeks—the very processes that have evolved to occur over the space of months.”
Even suicidal behavior might serve a design function. A small minority of researchers believe that we may have evolved to, under the right conditions, try to kill ourselves. Edward Hagen, an anthropologist at Washington State University, is one of the most vocal supporters of this idea, and he presented fresh support for it in the May 2016 issue of Evolution and Human Behavior. 5 He and two WSU collaborators, Kristen Syme and Zachary Garfield, set out to find evidence for two models of suicidal behavior, each of which cast suicide as a strategic behavior.
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The first model is called inclusive fitness, and it relies on the notion of the “selfish gene”: The most basic unit of reproduction in natural selection is not the individual organism but the gene. Your genes don’t care if you survive to reproduce, as long as they do, and they exist in more people than just you. So they might lead you, their host organism, to sacrifice yourself if it sufficiently benefits your family members, who share many of your genes. Hence, people seek to maximize not only their own fitness but, inclusively, that of their kin too. Most parents would decide in an instant to jump in front of a bus to save their children. And in studies of suicidal thinking, people frequently speak about not wanting to be a burden.
The second strategic model of suicidality is the bargaining model, which relies on the notion of “costly signaling.” 6 A colorful example of costly signaling is the peacock. Managing a big, eye-catching tail is costly, in that it wastes energy and draws predators. But the fitter a peacock, the less costly a big tail, and so big tails have evolved to signal genetic fitness to peahens. They are attractive not despite their costliness but because of it. In addition to communicating fitness, costly signals can also communicate need. Consider baby birds. They don’t need to chirp for food if their mother is right there, and chirping attracts predators, making it costly. But the more hungry or sickly a chick is, the less it has to lose by being eaten, and the more it has to gain by being fed. So chirping louder is an honest signal of greater need for food, and the mother responds. (Anthropologists and psychiatrists have long framed suicide attempts as cries for help, but considered them pathological forms of pleading rather than the results of context-sensitive and evolved cost-benefit analyses.) Whereas the goal of suicidality in the inclusive fitness model is death, the goal in the bargaining model is help. Crucially, the vast majority of suicide attempts are not fatal.
A small minority of researchers believe that we may have evolved to, under the right conditions, try to kill ourselves.
With these models in hand, Hagen and his colleagues analyzed 474 ethnographic records describing suicidal behavior in 53 diverse cultures around the world, looking for clues consistent (or inconsistent) with each model. Supporting the inclusive fitness story, 1 in 3 cultures had a record describing a suicide victim as a burden to others. In a few records, the victim was described as having low reproductive potential (due to advanced age or poor health), and in a few the victim’s survivors were described as being better off after a death. Against the model, however, many more records described family members as being worse off, and many victims were healthy.
In support of the bargaining model was the fact that those who had attempted suicide were often healthy, their attempts were often public and unsuccessful, and they often benefited. Three observations were most telling: First, victims had often suffered a threatening event, such as loss of a mate or resources, whose long-term repercussions depended on how others responded. Second, victims were often personally powerless. Third, they were often in conflict with those around them, thus looking for a bargaining tool. Overall, victims needed help solving a critical problem and weren’t receiving it. The authors provide a paradigmatic example of the bargaining model from a 1958 study of a people in Papua New Guinea:
Attempted suicide is punishable by a beating administered by the woman’s owner. Facts: The girl was being forced to marry a man she did not like. She attempted suicide several times in order to prevent the marriage. She was always saved from the river or captured on its bank. Outcome: Every time she attempted a suicide, she was beaten severely afterward. Since she did not stop, her brother and father consented to her marriage with Jok, whom she loved.
Hagen and his co-authors concluded that both inclusive fitness and bargaining are viable models of suicidality, each applying in different circumstances. “Hagen has proposed some really interesting and compelling theoretical models that fit with available data and may help to explain suicidal behavior from an evolutionary perspective—a long-standing puzzle in the field,” says Matthew K. Nock, an expert on suicide and self-injury at Harvard University. The evidence in the paper is not a clincher for either model—evolutionary theories, while often powerful, can also be slippery—but a few other studies lend additional tentative support to the bargaining model.
For example, the model predicts that depression—a leading risk factor for suicide—will be used as a bargaining tool most often when others will respond accommodatingly. In a 1987 study, people’s ratings of how upset they were with their social networks predicted their own level of depression, but only among those who found their networks generally helpful. 7 And in a 1997 study, fighting with their mothers or friends led women who’d just had an abortion to report greater depression and anxiety, but only if they described their mothers or friends as highly supportive. 8 Reacting to a social conflict with depression won’t work if the people around you won’t care. Depression can become a bargaining chip by risking the survival of one’s genes and one’s dependents, which should concern anyone invested in the sufferer’s health.
The bargaining model might also help explain why women are twice as likely as men to suffer depression. In a 2016 paper, Hagen and Tom Rosenström, a psychologist at the University of Helsinki, analyzed data on 4,192 American adults from an ongoing study by the CDC. 9 They hypothesized that because men are physically stronger than women, they’re more likely than women are to use anger as a bargaining tactic in social conflicts, whereas women are more likely to rely on depression. The data showed that people with greater upper body strength were less likely to suffer depression. What’s more, once the researchers took the effect of physical strength out of the equation, men and women were equally likely to be depressed. Hagen has written about post-partum depression in terms of costly signaling: A mother’s loss of interest in the health of herself or her newborn can act as leverage, recruiting the assistance of an insufficiently helpful mate or community. 10 Depression appears to be a tool (conscious or unconscious) for those who can’t muscle the support they need.
S o what should we do, based on these evolutionary models of depression? “I’m a bit hesitant to give advice based on my theories,” Hagen says, “because that would assume that my theories are true and therefore we’re ready to take this knowledge out of the lab and apply it clinically. I don’t think we’re at that point yet.” And if his theories are true, the picture is somewhat bleak, he says, in that there’s no easy fix. Treating depression will likely require resolving severe conflicts between you and your family, situations with no good guy and bad guy. In terms of therapy, clinicians might bring in patients’ family members to work through issues together, but many already do that—“So in practice a lot of what I’m saying isn’t radical,” he says.
These theories do cast some of our traditional responses to depression in a new light, however. If depression is a strategic response that we are programmed to carry out, consciously or unconsciously, does it make sense to try to suppress its symptoms through, say, the use of antidepressants? Hagen describes antidepressants as painkillers, arguing that it would be unethical for a doctor to treat a broken ankle with Percocet and no cast. You need to fix the underlying problem. He regrets the fact that the DSM, psychiatry’s diagnostic manual, has removed from major depressive disorder’s diagnostic criteria any exception for life circumstance, even bereavement. This is part of an effort to make diagnosis more objective and scientific, and encourage the profession to focus on observable symptoms rather than causes. 11
Even if depression evolved as a useful tool over the eons, that doesn’t make it useful today.
But in the case of depression, which often has clear preceding events, indifference to causality allows many appropriate patient responses to be categorized as disordered—and that flows directly from seeing depression as a breakdown rather than a strategic, evolved response. Prescribing antidepressants may improve a patient’s mood, but in the process prevent the patient from solving the underlying conflict and improving his or her mood even more in the long run. Depression usually doesn’t appear out of nowhere. It’s typically a response to adversity, with up to 80 percent of cases following major life events. The death of a woman’s close relative, for instance, was measured to increase their chances of suffering depression within the next month by 20 times.
The battleground over depression’s functionality may lie in those 20 percent of episodes without an obvious trigger. Perhaps you could say there’s some nonobvious cause, a conflict lurking in one’s psyche or latent in one’s family life. Thomas Joiner, an expert on suicide at Florida State University, says that “as episodes accrue, it can be harder and harder to find the trigger, but it’s usually there—triggers can be things like memories.” But since you can always point to something in your past with potential psychic consequences—that one time you got teased on the playground—the hypothesis that depression is an appropriate response to a stressful situation becomes nearly impossible to test objectively.
There’s another big caveat. Even if depression evolved as a useful tool over the eons, that doesn’t make it useful today. We’ve evolved to crave sugar and fat, but that adaptation is mismatched with our modern environment of caloric abundance, leading to an epidemic of obesity. Depression could be a mismatched condition. Hagen concedes that for most of evolution, we lived with relatives and spent all day with people ready to intervene in our lives, so that episodes of depression might have led to quick solutions. Today, we’re isolated, and we move from city to city, engaging with people less invested in our reproductive fitness. So depressive signals may go unheeded and then compound, leading to consistent, severe dysfunction. A Finnish study found that as urbanization and modernization have increased over the last two centuries, so have suicide rates. 12 That doesn’t mean depression is no longer functional (if indeed it ever was), just that in the modern world it may misfire more than we’d like. And of course some cases of depression would remain unexplained by evolutionary design. Peter Kramer, a psychiatrist at Brown University and the author of Listening to Prozac and Against Depression, notes that at least some episodes of depression are likely to be caused by genetic glitches or by negative thought patterns learned during previous unresolved episodes. Most sources, including Hagen, agree that depression is not one disease with one cause.
Inversely, even if depression and suicidality serve some purpose today, that doesn’t mean they evolved to do so. Randolph Nesse, a psychiatrist and the director of the Center for Evolution and Medicine at Arizona State University, raises this possibility with regard to the bargaining model. “Some people do use threats of suicide to manipulate others, just as they use threats of murder or exposing secrets,” he says, “but I don’t see these as specific adaptations shaped by selection. They are just some of the myriad ways people try to influence others.”
Nesse is even more dismissive of the inclusive fitness model of suicide: “There are many examples of animals sacrificing themselves for their kin, but I don’t see that suicide is one of them. Why not just go away?” Still, he says, the “broader perspective that there is something useful about low mood is, I think, the key to making progress and I wish more psychiatrists would recognize it.”
It’s clear that evolutionary models for depression have not won over the psychiatry community at large. According to Thomson, “My profession of psychiatry still views depression purely as an illness.” Insurance limitations have pushed many psychiatrists away from talk therapy and toward the more efficient prescription pad. So “there’s a lot of institutional and scientific investment in the exclusively disease model of depression,” Thomson says. “I’m basically telling colleagues they’re medicating people when they shouldn’t be. That’s not going to be welcome news.”
If Thomson, Hagen, and others are right that evolution has engineered us to be strategically depressed, our treatment strategies would need to change. Hagen sees depression as a social problem and not a medical problem. Andrews and a colleague, Paul Watson, describing the social navigation hypothesis, a theory that includes a version of the bargaining model, wrote in a 2002 paper that instead of prescribing drugs, “it may be best to let depression work its miserable yet potentially adaptive magic on the social network under protective supervision.” 13 And a greater attention to circumstance and cause would be warranted.
It’s hard for anyone to think about a condition as destabilizing as depression in impersonal evolutionary terms, particularly those who have felt its burdensome grip. I sometimes lament how much more industrious I would be without my own (now manageable) depression. But I also allow that, even today, my melancholia may have benefits. It focuses me on deeper questions of where I’m going in my life, even though—or, alas, because—it makes me question the value of anything and everything: including depression itself.
Matthew Hutson is a science writer who’s written for Wired, The Atlantic, and The New York Times. He is the author of The 7 Laws of Magical Thinking.
1. Kessler, R.C., et al. The epidemiology of major depressive disorder: Results from the national comorbidity survey replication (NCS-R). JAMA 289, 3095-3105 (2003).
2. Hagen, E.H. Evolutionary theories of depression: A critical review. The Canadian Journal of Psychiatry 56, 716-726 (2011).
3. Andrews, P.W. & Thomson Jr., J.A. The bright side of being blue: Depression as an adaptation for analyzing complex problems. Psychological Review 116, 620-654 (2009).
4. Watkins, E. & Baracaia, S. Why do people ruminate in dysphoric moods? Personality and Individual Difference 30, 723-734 (2001).
5. Syme, K.L., Garfield, Z.H., & Hagen, E.H. Testing the bargaining vs. inclusive fitness models of suicidal behavior against the ethnographic record. Evolution and Human Behavior 37, 179-192 (2016).
6. Hutson, M. The Power of the Hoodie-Wearing CEO. The New Yorker (2013).
7. Pagel, M.D., Erdly, W.W., & Becker, J. Social networks: We get by with (and in spite of) a little help from our friends. Journal of Personality and Social Psychology 53, 793-804 (1987).
8. Major, B., Zubek, J.M., Cooper, M.L., & Cozzarelli, C. Mixed messages: Implications of social conflict and social support within close relationships for adjustment to a stressful life event. Journal of Personality and Social Psychology 72, 1349-1363 (1997).
9. Hagen, E.H. & Rosenström, T. Explaining the sex difference in depression with a unified bargaining model of anger and depression. Evolution, Medicine, & Public Health 1, 117-132 (2016).
10. Hagen, E.H. The functions of postpartum depression. Evolution and Human Behavior 20, 325-359 (1999).
11. Hutson. M. In ‘Shrinks,’ Jeffrey A. Lieberman with Ogi Ogas Explore the History of Psychiatry. The Washington Post (2015).
12. Stack, S. The effect of modernization on suicide in Finland: 1800-1984. Sociological Perspectives 36, 137-148 (2016).
The lure of death: suicide and human evolution
At some point in evolutionary history, human beings came to understand, as no non-human animals do, that death brings to an end a person's bodily and mental presence in the world. A potentially devastating consequence was that individuals, seeking to escape physical or mental pain, might choose to kill themselves.
This article is part of the theme issue ‘Evolutionary thanatology: impacts of the dead on the living in humans and other animals’.
A late Roman ivory casket, in the British Museum, shows in sculpted relief two contrasting examples of humans who knowingly brought death on themselves (figure 1): Jesus, who had no desire to stop living, but who believed his death would benefit all mankind Judas, who had no thought of benefiting others, but who wanted to end his own intolerable guilt.
Figure 1. Panel from an ivory casket: the Crucifixion of Christ. Late Roman, AD 420–430. Copyright © The Trustees of the British Museum. All rights reserved. (Online version in colour.)
Suicide used to be called self-murder, felo de se. In an evolutionary context, the term murder is not inappropriate. Human beings have always been murderers, killers of other living beings. First, of course, killers of animal prey for meat, but also killers of other men and women. While not every ancient human would have had first-hand experience of assassination, everyone would have known and talked about it. Then, at some point, the idea must have dawned. Here's how the psychiatrist, Erwin Stengel has put it: ‘At some stage of evolution man must have discovered that he can kill not only animals and fellow-men but also himself. It can be assumed that life has never since been the same to him’ [1, p. 37].
The purpose of this paper is to consider just how radically life changed. I argue that the human mind must have had to evolve to a critical level of sophistication before anyone could arrive at the idea that ‘I can kill myself’. However, from then on, suicide would never have been far from people's thoughts. When times were hard, some individuals would have been bound to see death as an attractive option. Yet killing themselves would usually—if not always—have been a maladaptive act. I explore how this played out historically, and what remedies, if any, were available.
2. ‘I can kill myself’
It's simple to say, it's a discovery made by every growing human, but the thought of killing oneself will usually have complex layers. Clearly, it has to begin with imagining the act: you have to have a picture of how it can be done. Stengel implies that early humans acquired this from observing how animals and fellow-humans could be killed. But this hardly seems probable. The fact is most of the ways you might observe to be effective for killing another—be it with teeth or claws or fists or clubs—would not be feasible ways for you to kill yourself. Instead, for most of human history (until the advent of modern murder weapons such as guns), a more likely model for suicide will have been accidental death: falling from a cliff, drowning in a lake and bleeding to death from a cut. By imagining yourself in the victim's place, you would see that what happened to him or her by accident could happen to you by your own intent. You might still want confirmation that it can really be done. But, for this, you might not have to look far. In a typical human community, where suicide is already prevalent, you will have heard tell of others who have successfully killed themselves. Humans as a species are notoriously imitative. Perhaps, every suicide is at some level a ‘copy-cat suicide’ (which I'll return to later in the paper.)
But, now, to go deeper: when you think ‘I can kill myself’, who is this ‘self’ and what do you imagine will result from ‘killing’ it? Again, Stengel implies that early humans would have understood the inevitable consequences of self-killing from observing the killing of others. Bodily death, however caused, has effects that anyone can see and take on board. There's the obvious bodily decay. But the most salient change is in the dead person's role as an actor in the physical or social world. They will not be coming back. This is a fact of death that non-human animals with complex social lives can also understand up to a point. Frans de Waal describes how, when a group of chimpanzees in the Arnhem Zoo were shown a video film of the alpha-male, Nickie, who had died by drowning 2 years earlier, his erstwhile rivals panicked as if they had seen a ghost [2, p. 214]. By applying this to your own case, you would realize that you yourself once dead will no longer participate directly in the lives of others.
But we must go deeper still. For there is, of course, another meaning of ‘self’, and hence, the probability that self-killing will have a still more significant result. When your body dies, what happens to your mind? Once you are no longer an actor in the public realm, can you no longer be a thinker or feeler in the private one? This is not of course something you or anyone else can discover from direct observation. But it is perhaps something you can deduce from circumstantial evidence. As a human, with a ‘theory of mind,’ you expect to be able to infer another person's mental state from their outward behaviour. When, now, you observe that an individual's body no longer behaves in any way at all—it neither acts spontaneously nor reacts to your probes—you have very good reason to suppose there is no longer anyone at home inside. True, absence of evidence is not entirely reliable as evidence of absence. But, in fact, you yourself have had plenty of direct experience of your own mind going absent at a time of pseudo-death. When you fall asleep, and your body becomes motionless and unresponsive, you know for a fact that your mind temporarily vanishes. You may remember how as a child you cried yourself to sleep and found blessed relief in the ensuing oblivion.
Thus, kill yourself, and the result will be that in every important respect you will have removed yourself from the world. Like the parrot in the famous Monty Python sketch, once dead, you will have ceased to be you will be an ex-human being.
3. The path to suicide
So, to return to Stengel, ‘at some stage of evolution’, humans made this momentous discovery. I hesitate to put a date on it. But given the cognitive skills required—counterfactual reasoning, mental simulation, time travel and theory of mind—I'd say no one would have been able to make the discovery until ca 100 000 years ago. Soon after that, however, just about everyone was able to make it. And since then ‘life has never been the same’.
The question is what the practical impact would have been. There seems no reason to doubt that the thought of self-killing would soon enough have been translated into action. Some of those who discovered they could kill themselves would have chosen to kill themselves. Suicide leaves no trace in the archaeological record. But modern day statistics presumably throw light on past history [3,4]. Today no fewer than 1.4% of all deaths worldwide are attributed to suicide, making it the world's leading cause of violent death. Across the world more people—some 800 000 yr −1 —die from suicide than all wars and homicides combined. Many more make the attempt. In total, 2.7% of the world's population have tried to take their own lives. Even more plan it. Fourteen per cent, of report, have had suicidal ideation at some stage.
These figures are enough to make any demographer sit up and wonder. How could self-destructive behaviour on this scale have been persisting at such a high frequency? What does this suggest about the effects—good or bad—of suicide on human fitness? Common sense would say that self-killing must be the ultimately disadvantageous act, a sure path to genetic oblivion. But maybe this is wrong. Could suicide be biologically adaptive after all?
As I implied at the outset, there would seem to be two broad classes of suicide, distinguished by their motivation: those concerned with benefiting other humans and those concerned with benefiting primarily the one who dies. We can call these, as Émile Durkheim did (but without necessarily buying into his theoretical framework), ‘altruistic’ and ‘egoistic’ suicide. I want to suggest they can be distinguished at another level: they correspond to the two different conceptions people have of what their death will immediately achieve.
When someone kills themself in order to remove their bodily person from the world, it would seem quite plausible that they believe the knock-on effects will improve things for others. Jesus dies on the cross in the hope that by this public sacrifice he can bring about the salvation of all mankind. Or, for a more straightforward example, Captain Oates stumbles out from his cabin to die in the snow in the hope that, by relieving other members of Scott's polar expedition from the burden of supporting him, he can give them a better chance of survival.
This is altruistic suicide. Could it be biologically adaptive? It clearly could be if it does, in fact, benefit the subject's kin or social group. In one of the earliest statements of the principle of kin selection, Haldane is reported to have said ‘I would gladly give up my life for two brothers or eight cousins' [5, p. 496]. Humans do not, like social insects, have a propensity for specific acts of suicide hardwired into their brains. But humans are nonetheless genetically primed with feelings of love and obligation for family and friends. Many theorists accept that this could partly explain why humans are willing to sacrifice themselves for the common good—in times of famine, or plague or war. It might also help explain cases of apparent ‘suicidal generosity’, as when individuals choose to die—or even submit to being ritually killed—when they have become too old and decrepit to carry on. By relinquishing their bodies in such circumstances, they could certainly be adding to their inclusive fitness. So, there might indeed be positive selection for psychological traits that abet the decision .
What, however, when someone kills themselves in order to remove their own mind from the world? Then, it is in no way plausible that they are thinking of benefiting others. The much more likely motive must be that they believe they themselves will be better off as a result. Thus, Judas Iscariot hangs himself because he cannot live with his internal sense of shame. An Indian chieftain's daughter jumps to her death from a cliff rather than marry a man she does not love. A businessman drowns himself when his company fails.
This is egoistic suicide. And it's in many ways the opposite of altruistic. Far from wanting to help others, these self-killers are thinking primarily of personal escape. They either don't care about the effect on others, or sometimes even intend some kind of vengeance. And, whether they intend it or not, the effects on family and friends are often devastating.
Now, from an evolutionary viewpoint, here's the problem. Across the world the great majority of suicides are egoistical. Anthropologist Charles MacDonald, reviewing the motives for suicide, concludes: ‘A cross-cultural comparison shows that grief over, and conflict between closely related people, together with sheer physical pain and discomfort, cause or promote suicide more often than any other circumstances' [7, p. 427]. ‘The victims simply want to go. They don't mean to change things … The suicide wants to stop hurting’ [8, p. 221]. Edwin Schneidman, from a clinician's perspective, observes that the common goal of suicide is cessation of consciousness. He writes: ‘the idea of cessation—that you can be free of all your problems, get out of this mess, cancel your debts, release yourself from this anguish, stop this disease is the turning point in the suicide drama’ [9, p. 13].
Could this type of suicide possibly be adaptive? Surely no amount of special pleading could make it so. Many of those who do it are young. Across the world, it is the second most common cause of death in teenagers. If these young people had not died by their own hand, they would almost certainly have got over the hurt and gone on to make a success of their lives. At a stroke, they have ruined their own fitness and that of related individuals too. At the level of biology, egoistic suicide is clearly a mistake, a path to genetic extinction.
So, what's going on? How can it be that so many continue to die this way? The authors I've just quoted point to the obvious explanation. Yes, it is indeed a biological mistake. But it is precisely because humans rise above biology that they can make this mistake. For, at a rational psychological level, it is not a mistake at all. Humans like all animals have an instinctive drive to escape from pain, emotional as much as bodily. When they experience ‘psychache’, as Schniedman calls it , when they feel sad, jealous, unloved or inadequate they will do whatever it takes to make these feelings go away. But for humans, unlike animals, the question of how to escape has been left open to reason. Given their insight that killing themselves will put an end to their suffering, suicide can seem to provide a perfectly rational solution: a reliable method of self-euthanasia. Nothing hurts less than being dead.
Moreover, when other possible escape routes would involve time and effort, suicide can seem to provide a solution that is quick and easy too. It may, as I noted above, require intelligence to think of it, but its realization can be simplicity itself. It requires no special expertise to leap from a cliff, to drink poison or to slit one's wrists. In parts of Asia, people are known to ‘hang’ themselves simply by kneeling and leaning into the rope [8, p. 208].
Susan Sontag has written ‘How thin the line between the will to live and the will to die. How about a hole … a really deep hole, which you put in a public place, for general use. In Manhattan, say, at the corner of Seventieth and Fifth. A sign beside the hole reads: 4 PM--8PM/MON WED & FRI/SUICIDE PERMITTED. Just that. A sign. Why, surely people would jump who had hardly thought of it before’ [11, p. 116]. And indeed, real suicides are often unplanned and impulsive. A survey of 306 Chinese patients who had been hospitalized following a suicide attempt found that 35% had contemplated suicide for less than 10 min and 54% for less than 2 h .
Schneidman's term psychache may suggest major distress. But the precipitating causes for impulsive suicide can actually be astonishingly trivial. A recent review in Science about suicide in otherwise normal people opens with this example: ‘A young mother and loyal wife, Mrs Y showed none of the standard risk factors for suicide. Villagers said she exuded happiness and voiced few complaints. But when a neighbor publicly accused Mrs Y of stealing eggs from her henhouse, the shame was unbearable. Mrs Y rushed home and downed a bottle of pesticide’ . In 2016, Jacintha Saldhana, a nurse in charge of the Duchess of Cambridge in a London hospital, hanged herself, a day after accepting a hoax telephone call from a radio station. In the new world of social media, it is all too common for a schoolgirl to overdose on sleeping pills because she is being bullied on Facebook.
So, people kill themselves ‘when they want to go’: sometimes after careful reflection, sometimes on the spur of the moment, sometimes for profound reasons and sometimes for shallow ones. Hamlet asks ‘who would bear the whips and scorns of time, the oppressor's wrong, the proud man's contumely, the pangs of despised love, the law's delay, the insolence of office, and the spurns that patient merit of the unworthy takes, when he himself could his quietus make with a bare bodkin?’ The answer is, evidently, by no means everyone.
The trouble is everyone has moments of despair. It is a grand, if tragic, truth about the human condition that—just because humans have so much higher ambition than other animals—hurting is bound to be a part of life. The poet Cesare Pavese said it explicitly, ‘everyone has a good reason for suicide’ [13, p. 99]. The philosopher Wittgenstein once told a friend that ‘all his life there had hardly been a day in which he had not thought suicide a possibility’ [14, p. 155]. More typically, among today's American high school students, 60% say they have considered killing themselves and 14% have thought about it seriously in the last year . George Santayana spoke for too many, when he wrote: ‘That life is worth living is the most necessary of assumptions and, were it not assumed, the most impossible of conclusions' .
5. Fear of death?
We have to stop to consider. Humans have evolved to this point: a point where a significant number live near the threshold of a self-generated catastrophe. Surely, this cannot be where evolution has rested? If the threat is as great as I've suggested, would not natural selection have come up with ways of countering it? Why have humans not evolved to have better innate defences against suicide built into their minds?
There is, of course, one level of defence we might expect to have been there from the beginning. This is a natural fear of death. Geoffrey Miller has written: ‘There is no way to escape the hardwired fears and reactions that motivate humans to avoid death. Suffocate me, and I'll struggle. Shoot me, and I'll scream. The brain stem and amygdala will always do their job of struggling to preserve one's life at any cost’ (). Ernest Becker has famously said ‘the fear of death haunts the human animal like nothing else’ ([18, p. xvii]). If, as these authors imply, the fear of death is an evolutionarily ancient animal fear, then presumably it would always have provided an important last-ditch barrier to human suicide. In fact, its existence ought to mean that the thought ‘I can kill myself’ must usually be something of an empty boast.
I have to say I am sceptical. And not just because people do, in fact, kill themselves, sometimes almost casually. I think there is actually precious little other evidence that humans have a naturally evolved fear of death. I don't disagree, of course, with Miller that humans have hardwired fears that motivate them to avoid situations that could put them at risk of dying—pain, anoxia and so on. They do instinctively recoil from pain and thus will certainly do what they can to avoid a painful death. That's why, for example, many people when terminally ill will choose—if only they are allowed to—to be ‘put to sleep’ rather than to endure the agonies of cancer. For the same reason, those intent on suicide will take precautions to prevent instinctive fears thwarting their attempt. A case in point is David Kelly, the scientist who exposed the British Government's lies about Iraq's weapons of mass destruction. He took 29 tablets of the painkiller co-proxamol before he slit his wrists.
So, no question, people often fear dying in pain. As Woody Allen said, they don't want to be there when it happens. However, if and when death is inevitable, but likely to come easily, all the evidence suggests that people generally take it remarkably calmly. The German photographer, Walter Schels, has made photos of people in the terminal stages of illness, shortly before they died, and the day after. The 26 sitters for these portraits were asked how they felt about dying. They had mixed emotions: sadness, relief and resignation. But not one of them showed fear. Annoyance was more like it. One of them, Klara, remarked: ‘I'd only just bought myself a new fridge-freezer. If I'd only known’ [19, p. 106].
Ah, some theorists say, but the lack of overt fear is due to some form of denial. When humans contemplate death, they do become scared momentarily, but then according to ‘Terror Management Theory’ they immediately suppress it . Or they deny the truth of the facts that would otherwise cause them to be scared . But I believe there is a more straightforward explanation. This is that fear of death simply does not exist, as an evolved adaptation, either in humans or in any other animals.
How could that be? Why wouldn't such a useful fear have evolved, especially once humans discovered death's fuller meaning? I suggest the answer is that the ancient fear system was simply blind-sided by the discovery. There had never before been occasion to respond to any such nebulous concept as the ‘idea of death’, and now it presented special difficulties. How was natural selection to get to grips with a hypothetical state of not being? True, there are lesser states of notness that humans have had no trouble adapting to. They can and do have a natural fear of not being fed, not being warm, not being loved. But not being at all, not existing? This was just too elusive a concept.
I look at it this way. It's a general principle of evolution that any behaviour that can be learned by an individual through extended practice can be adopted by selection and become innate. So, for example, people can readily learn to fear not being fed, by experiencing famine a few times. They can learn to fear not being loved, by experiencing abandonment. And so on. What's more, they can learn such fears vicariously, by sharing what others have been through. In these cases, selection could quite well have followed in learning's path. But death is different. No one could learn to fear death through practice: ‘Hey, I've just visited the other side. I'm not going there again!’ Nor will there be anyone else whose experience they could draw on.
This said, we should not assume that human suicide was destined to remain unopposed. If nature was unable to arrange things so that people instinctively feared dying by their own hands, then perhaps human culture could step in to arrange it. Or, as a completely different strategy, perhaps the threat of suicide could be answered by developing a new-found appetite for staying alive. I'll consider in a moment how culture may indeed have weighed in to supplement biology.
6. The suicide meme
But first, let's take a further look at the size of the problem our ancestors faced, for we have not yet revealed the full scale of it. At the critical juncture in prehistory, when the understanding of self-killing first surfaced, just how vulnerable would early humans have been? As far as I know, no palaeo-anthropologist has ever thought to ask. But I'd say we should assume the worst. To start with at least, people would have had no kind of immunity to suicidal thoughts. In which case it's realistic to imagine a scenario where suicide would have spread like measles in an unprotected population. And, indeed, measles is an alarmingly apposite analogy, because, as contemporary evidence shows, even today the suicide ‘meme’ is highly infectious. It jumps all too easily from one mind to another.
As Durkheim noted: ‘Suicide is very contagious … There is the well-known story of the fifteen patients who hung themselves in swift succession in 1772 from the same hook in a dark passage of the hospital’ [22, p. 97]. I suggested earlier that almost all suicides may be copy-cats. But suicide contagion is something more: copying with positive feedback. It has been dubbed the ‘Werther effect’ after the hero of Goethe's novel, The sorrows of young Werther, who kills himself after falling hopelessly in love with a married woman . Following its publication in 1774, there were hundreds of imitative deaths across Germany.
Recent research has confirmed just how strong the effect is . Every time a celebrity suicide is given exposure in newspaper or TV, the copy-cats follow. It is estimated that Marilyn Monroe's death, in August 1962, was responsible for 200 extra suicides within a month. After a popular South Korean actress hung herself in 2008, suicides jumped 66% that month, with young hanging victims accounting for most of the increase .
But 66%, that's nothing. There are still parts of the world today where rates of suicide are 10 times the average elsewhere, apparently as the result of local chain reactions. MacDonald's research, among the generally contented people on the island of Palawan in the Philippines, found evidence of waves of suicide spreading through small villages. In a recent study, Jollant & MacDonald undertook a psychological autopsy of the individual victims to try to uncover predisposing factors . It turned out that much the most significant risk factor was having had a close relative die from suicide. MacDonald comments: ‘The child grows up accustomed to the idea. He/she sees or hears about elders, uncles, aunts, older cousins, and friends' parents killing themselves … Thus suicide becomes an accepted model of behaviour, an option open to the individual’ [8, p. 264]. Note how the thought ‘I can kill myself’ can then take on an added meaning: ‘I can’, not only in the sense that it is practicable, but that it is permissible.
What can have happened on Palawan to get the chain reaction started? MacDonald believes that suicide was at a ‘normal’ level until early last century some kind of disaster struck—a cholera epidemic, a slave raid—that wrecked the villagers' lives. This caused a surge in suicides, and the wave has been propagating ever since.
So, to ask it again, how prevalent might suicide have been among our ancestors? Suppose it's true that they first became at risk ca 100 000 years ago. To begin with, the incidence might have remained relatively low. However, once humans left Africa, living conditions were set to become increasingly harsh. In the icy climate of central Europe 50 000 years ago, with people battling the elements and in murderous competition with their neighbours, there would have been plenty of occasion for short-term despair. If then the rate of suicide reached a critical level, it could have become epidemic. Who knows, but that suicide threatened the very survival of whole populations. There have been several genetic bottlenecks in human history, suggesting that populations crashed almost to nothing. These have been attributed to factors such as internecine strife, volcanic winter or disease. But, perhaps, the real cause was this worm inside the human mind.
7. Cultural barriers
Still, here we all are today. Against the odds, our ancestors as a species evidently managed to pull through. Given that natural anti-suicide defences were absent or slow to evolve, what else could have brought the epidemic under control? Presumably, the best hope of developing timely and transferable defences must have been human culture. Here, I have to say, the picture is complicated and not well researched. But at least some of the more recent cultural barriers to suicide are in plain view .
In historical times, religious authorities have repeatedly issued anathemas against suicide. Mediaeval Christianity decreed it to be a mortal sin. Self-murderers would not be given decent burial, but rather be buried at a crossroads with a stake through the heart. In all modern states, until recently, suicide and attempted suicide have been considered to be crimes under the common law. The successful perpetrator's possessions could be confiscated, and the unsuccessful one imprisoned. In some places, the party supposed to have provoked the suicide—by spurning a love-suit, say—could also face a penalty. In the UK, attempted suicide was not decriminalized until 1961. In the 10 years pre-1961 nearly 6000 people were prosecuted, of whom 5400 were found guilty, and imprisoned or fined. It was common practice in the 1950s to have a policeman sitting at the bedside of an unconscious patient in A and E, waiting to interview them.
There have also been attempts to limit the spread of the suicide meme by limiting exposure to it. In Europe, after the effect of Goethe's book became apparent, it was soon banned in several countries. In Germany, it was even forbidden to dress like Young Werther in blue coat and yellow trousers. In most countries today, there are strict guidelines for the Press intended to play down the reporting of suicide—to keep it off the front page and avoid sensational headlines.
These are deliberate measures, with suicide directly in their sight. But there are also cultural practices that can work to deter suicide without targeting it so deliberately. One obvious and important way is by instilling beliefs that are incompatible with the premise that can make suicide so appealing to someone who wants to escape: namely, the belief—the hope—that death will bring about mental oblivion. The world over, humans have invented systems of religious belief that explicitly promulgate the idea of the mind continuing after death. What's more, the Abrahamic religions, in particular, make a point of threatening that the afterlife for sinners, and suicides especially, will be an unpleasant one.
Now, even though humans may not be set up by nature to fear the nothingness of death, they can quite easily be set up by culture to fear the somethingness of an afterlife. The threat of hell fire can certainly set the amygdala ringing. But it needn't be so specific as fire. It could be just the threat of strangeness, the unknown. Think of Hamlet, contemplating suicide:
But that the dread of something after death,
The undiscover'd country from whose bourn
No traveller returns, puzzles the will
And makes us rather bear those ills we have
Than fly to others that we know not of.
I'm not suggesting that the idea of a horrible afterlife was ever invented specifically to deter suicide. But if, as is surely the case, it has consistently worked to this effect, this is presumably a reason why it has taken such a hold. Some humans undoubtedly owe their lives to it.
It's evident how culture has found ways to weigh in against suicide on several levels. The measures are by and large negative ones. They are clearly not wholly effective. But there's no question they can and do work as a deterrent. The fact that suicide rates are lower in Muslim countries, for example, presumably has something to do with Muslim teachings about hell. As the exception that proves the rule, the villagers of Palawan are reported to have largely lost any faith in an afterlife .
But does deterrence have to be the only strategy? Wouldn't we expect more positive methods to have evolved as well? In place of punishment or censorship or threats, why not oppose a destructive mind virus with a redemptive one?
The English priest Chad Varah founded the Samaritans in 1954, a group dedicated to talking suicides down, simply with words of reassurance. The message ‘There is hope’, posted on the bridge or beside the railway track, may seem to verge on the banal. But, in fact, this is the one message that human society might long ago have discovered it can give with confidence. Research shows that in nine cases out of 10, the hurt isn't going to last. Daniel Gilbert, author of the book Stumbling on Happiness, advises: ‘Few of us can accurately gauge how we will feel tomorrow or next week … We expect to feel devastated if our spouse leaves us or if we get passed over for a big promotion at work. But when things like that do happen, it's soon, “She never was right for me”, or “I actually need more free time for my family”. People… mistakenly expect such blows to be much more devastating than they turn out to be’ .
The lesson is simple: ‘Don't jump now, because it's not what your future self would choose’. Have humans had to wait for a Harvard psychologist to tell them this? Thankfully, not. The message is implicit—presumably for a good reason—in much of the hand-me-down wisdom of our folk cultures: the stories, songs, proverbs and so on, that are there to remind people if ever they doubt it that life is worth living after all.
8. Sensory consciousness
What does make life worth living? The poet Byron wrote ‘The great object of life is sensation, to feel that we exist even though in pain’ [28, p. 28]. I suggested earlier that, in the course of history, suicide might have been countered by some newly evolved appetite for staying alive. Humans collectively might have come up with some knock-down philosophical argument to chase away Santayana's scepticism. Maybe so, though we have yet to see it. But how much more promising, at the level of the individual, if natural selection acting on human genes could have found an answer internal to the self. Could mere—mere?—sensory consciousness have been refashioned in the course of human evolution just so as to make people pause before they seek oblivion?
‘There's night and day, brother, both sweet things sun, moon, and stars, brother, all sweet things there’s likewise the wind on the heath.’ The words are from Lavengro, the autobiographical novel of the Victorian adventurer George Borrow. As Borrow tells it, he has been reading Goethe. He's toying with the idea of suicide. He gets into conversation with a Romany gypsy, Jasper, whom he has befriended on his travels. ‘What is your opinion of death?’ says Borrow, as he sits down beside him. ‘Life is sweet, brother, who would wish to die?’ ‘I would wish to die’, says Borrow. ‘You talk like a fool’, says Jasper. ‘Wish to die indeed! There's the wind on the heath, brother if I could only feel that, I would gladly live for ever’ [29, p. 180].
It strikes a deeply human chord. We get it. But stop to consider just how unexpected this is. How come these sweet things—‘the sun, moon and stars', ‘the wind on the heath’—can be reasons not to kill ourselves? How come we humans are so awestruck by sensory experience ?
The phenomenal quality of consciousness is widely regarded as a mystery. I've argued in my book Soul dust  that its very mysteriousness is an adaptive feature. The seemingly magical qualities of sensation—the redness of red, the saltiness of salt and the paininess of pain—have been specifically designed by natural selection to impress us with their inexplicable out-of-the-world properties. Human consciousness on this level exists as a biological adaptation precisely to ‘change the value we place on our own existence’ .
I've been taken to task by critics for suggesting that any biologically evolved organism could need a reason to live over and above the imperatives of life itself. But human beings are not any organism. They are the first to have had to wonder whether it's all worthwhile. We've seen in this paper the dark side. If there's a bright side, it may be that humans have come to live—perforce—in a strikingly beautiful world.
Recall Plato's golden string by which we are granted the strength and opportunity to pull back against the control of the gods. Substitute genes for gods and you get an oversimplified evolutionary perspective. Substitute the constraints of society and the inevitability of death for gods and you get an oversimplified existential perspective. Neither discipline has suggested an alternative to Plato's rational rope, although each is critical of it. Thus, existentialists are especially prone to denigrate the value of dry, abstract reason, and it is no coincidence that one of the best lay person's introductions to the discipline is titled Irrational Man ( Barrett 1958). For their part, sociobiologists are quick to point out that reason itself is an adaptation and, as such, situation-specific and often blinkered. The human brain, after all, is a biologically generated organ concerned with maximizing the fitness of its bearer and the genes that created it, not necessarily with conveying an accurate picture of the real world.
The prospect remains, however, that human beings, despite their biological baggage, retain enough freedom to fashion their own lives and their own future. “The greatest mystery,” according to André Malraux (1989), “is not that we have been flung at random among the profusion of the earth and the galaxy of the stars, but that in this prison we can fashion images of ourselves sufficiently powerful to deny our nothingness.” Should anyone doubt the capacity of human beings to deny their nothingness and define themselves (if necessary, counter to their evolution-given tendencies), I conclude with a thought experiment that is homey, homely, even scatological, but that should reassure everyone that Homo sapiens possesses abundant room for existential freedom.
Begin with this question: Why are human beings so difficult to toilet train, whereas dogs and cats are housebroken so easily? Take evolution into account, and the answer becomes obvious. Dogs and cats evolved in a world in which it was highly adaptive for them to avoid fouling their dens. Human beings, as primates, evolved in trees such that the outcome of urination and defecation was not their concern but, rather, a potential problem for the creatures down below.
But are people, who—similar to dogs and cats—live on the ground, doomed to wallow in their excreta, hopeless and helpless victims of this particular aspect of their human nature? Not at all. Although it requires going against eons of evolutionary history and a deep-seated primate inclination (or disinclination), human beings are able to act in accord with their enlightened self-interest. For all its mammalian, evolutionary underpinnings, a primate that can be toilet-trained reveals, ironically, a dramatic capacity for freedom, maybe even enough to satisfy the most ardent existentialist.