Information

When did our ancestors switch to a menstrual cycle instead of the estrous cycle?


The Wikipedia page on the Estrous cycle says:

Humans have menstrual cycles instead of estrous cycles. They shed their endometrium instead of reabsorbing it. Unlike animals with estrous cycles, human females are sexually receptive throughout their cycles.

The page on the menstrual cycles says:

The cycle occurs only in fertile female humans and other female primates

Do we know how many million years ago that switch happened and our female ancestors got sexually receptive throughout their cycles?


Menstruation occurs only in most of the primates, and a handful of other mammals. It is tempting to speculate that place the switch to menstrual cycles evolved right after the split between non-menstruating primates (tarsiers and their relatives) and menstruating relatives (almost all others), which is about 63 million years ago.

There are other menstruating animals, so I am not sure if nature reinvented menstruation whenever social conditions required unproductive sex, or menses are in fact a more archaic trait.

I doubt we have material evidence about all these speculations.


How did menstruation become taboo?

Why don’t we call menstruation by its name? Euphemisms serve a purpose. They give us words to talk about things that are considered culturally taboo. The impact of typical menstrual taboos is clear: they can lead to significant challenges in menstrual management, adverse reproductive health outcomes, social ostracizing, disease, and even death.

Menstruation stigma is a form of misogyny. Negative taboos condition us to understand menstrual function as something to be hidden, something shameful. And by not naming a thing, we reinforce the idea that the thing should not be named.

But have periods always needed code words? Where did these words come from, and how did they come about? Were periods always considered a negative experience?

Menstrual euphemisms and taboos are old. But not all societies view menstruation negatively.

Menstrual taboos are found in the Quran:

“go apart from women during the monthly course, do not approach them until they are clean” Quran 2:222,

“…in her menstrual impurity she is unclean… whoever touches…shall be unclean and shall wash his clothes and bathe in water and be unclean until evening” Leviticus 15

…and in the first Latin encyclopedia (73 AD):

“Contact with [menstrual blood] turns new wine sour, crops touched by it become barren, grafts die, seed in gardens are dried up, the fruit of trees fall off, the edge of steel and the gleam of ivory are dulled, hives of bees die, even bronze and iron are at once seized by rust, and a horrible smell fills the air to taste it drives dogs mad and infects their bites with an incurable poison.” (1).

Taboos are likely pre-agricultural, pre-modern-brain, and likely even pre-language (2, 3).

Menstruation, after all, far predates language. Our lives as the earliest evolving humans centered around survival, reproduction and biological functions: birth, death, sex, hunting. These elements were central in shaping language, not the other way around. And that’s where anthropologists do their research into menstrual taboo: at the intersections of evolution, behavior, and biology.

But while menstrual negative taboos are nearly universal, there are exceptions, and taboos themselves are variable. Certain societies operate with positive menstrual associations and euphemisms. Some modern-day hunter-gatherer societies, for example, hold an understanding of menstruation as being powerful, healing, protective and sacred (4, 5). These groups are also more likely to have a degree of gender egalitarianism (2, 5).

Some menstrual customs can act as tools that enhance female autonomy, granting social control and relief from work, among other benefits (4, 6, 7). The Mbendjele tribe of Central Africa, for example, still uses sayings like “my biggest husband is the moon” (8). The biggest grass hut of the Mbuti tribe in Zaire is the menstrual hut, where women go when they have their first period, accompanied by other girls and female relatives. There, having a period is considered powerful and blessed by the moon (9).

Even ancient Egyptian medical texts, including the Kahun Gynecological papyrus,

1800 BCE, and the papyrus Ebers

1500 BCE, use the word hsmn for menstruation, which, some argue, also meant “purification” (7). Menstruation, in these texts, is seen positively. Cures for amenorrhea are offered, and menstrual blood is used as an ingredient in ointments, like in one for saggy breasts (hmph)(10, 11).

The creation of menstrual taboos took place independently and repeatedly across different peoples and geographies. But scholars don’t agree on why this happened.

The origin (and function) of negative menstrual taboo is still debated. Freud said it was our fear of blood (12). Allan Court argued the taboo began, in part, because early humans found menstrual blood to be soiling (or, as he put it in 1963, having “a depressive effect on organic materials”) (13). Anthropologist Shirley Lindenbaum theorized in 1972 that taboo was a form of natural population control, limiting sexual contact with “pollution” stigma (14). In 2000, Historian Robert S. McElvaine coined the term non-menstrual syndrome or NMS to describe the reproductive envy that led males to stigmatize menstruation, and to socially dominate women as “psychological compensation for what men cannot do biologically” (15).

All of these theories are tied to the time and place in which they were developed, and many were formed with a presumption of menstrual negativity. Clellan Ford postulated that the menstrual taboo was developed because early societies knew of its “toxic, disease-causing effects” (16). Of course, we now know that menstrual blood is not toxic. But this view persisted in science through the 20th century. In 1920, Dr. Bela Schick coined the term menotoxin after concluding that flowers handled by a menstruating nurse wilted more quickly (5). Harvard researchers Olive and George Smith (pioneers in the fields of gynecology and estrogen treatment) injected animals with bacteria-latent menstrual blood in 1952, killing them (16). According to The Curse: A cultural history of menstruation, the Smiths continued to attribute the deaths to a menotoxin for several years, even after other research found that the animals died from bacterial contamination of the blood, rather than the blood itself (17). Menstrual blood toxicity was disproven in the late 1950s (18).

In 1974, a comparative study of 44 societies found a majority of cultures surveyed viewed menstruation, in part, as what it is: a signal for a reproductive phase. The study also found that the appearance of taboo in a given society may be closely tied to how much or little males participate in that society’s procreative activities, like child rearing and childbirth — that is, higher participation was associated with fewer taboos (though this relationship does not speak to causation)(5).


History of Ancient Human Sleep

Neolithic Era

The absence of a bright night sky and the threat of predators meant that our Neolithic ancestors (around 10,200 BCE) went to bed a couple of hours after dusk. What makes this group different from our Paleolithic predecessors during the Stone Age is that this cohort tried to make their bedtime space more habitable. The heaps of straw that used to serve as beds began to be replaced by raised surfaces.

8,000 BCE

Technology continued to advance but at a slow rate. Archeologists have discovered ancient sleeping abodes that were circular and more like nests than beds. The circular shape of these makeshift beds suggests that the fetal position was most preferred.

1300s – 1600s

As we enter the middle ages, sanitation became an issue. Monty Python’s comedy, Monty Python and the Holy Grail described conditions as “damp, smoked out, and filthy.” Even the wealthy lived in smelly filth as populations exploded and the crowded living areas had no plumbing.

Some cultures, however, had begun to explore the idea of more comfortable sleeping arrangements. Bedframes with stuffed mattresses became common. Early materials were straw and down made nights more peaceful.

Renaissance

Known for its art and societal advances, the Renaissance period experienced a revolution. The rough cloth and straw mattresses were now covered with velvet and silk, which added an air of luxury.

Earlier references had been made to the idea of biphasic sleep (Homer’s Odyssey, for example), but now mentions began to show up in more literary works. It was considered a regular habit among civilization during this time to have a first and second rest period during the night while experiencing a peaceful waking segment in between.

Instead of feeling concern over being awake during the middle of the night, citizens would use this time for prayer, reflection, sex, chores, reading by candlelight and visiting friends.

Industrial Revolution

Long working days and regimented factory schedules meant that people could no longer enjoy a leisurely period of rest between sleeping sessions. Instead, for efficiency, they began compressing their shuteye into a single cycle.

19th Century

With the advent of publicly lit streets and the invention of electricity, urban residents and the upper classes have shifted away from a biphasic schedule. They’re beginning to become more conscious of the passage of time and the efficiency that should be afforded during waking hours. Doctors started recommending a single session of slumber instead of two distinct periods.

By the 1920s all reference to a biphasic or segmented sleep schedule have entirely ceased.


When did our ancestors switch to a menstrual cycle instead of the estrous cycle? - Biology

Monday marked the 50th anniversary of the intervention of the birth control pill. There is no doubt that the pill has had a huge influence on sexual attitudes, sexual activity, and how much control women had over their own fertility. The pill, although it may not be the right choice for everyone, should be celebrated for these reasons. But there is something else to consider here: how did the invention of the pill shape the way that women (and the medical community for that matter) view periods?

When you think of the pill, the first image that comes to mind is that iconic little container of pink and white pills that represents one menstrual “cycle.”

In Malcolm Gladwell’s fantastic article, John Rock’s Error, Gladwell explains how the invention of the pill was heavily influenced by the Catholic Church. One of the creators of the pill, a devout Catholic, wanted it to be viewed as “natural” since it used chemicals that naturally occur in the body to prevent pregnancy. It was necessary, then, for women to continue to have their period regularly to show that the pill did not interfere with a woman’s menstrual rhythm.

But, speaking from an evolutionary standpoint, there is nothing natural about having a menstrual period every month because it is not natural to limit fertility. Our female ancestors spent a good portion of their reproductive years pregnant and not having a period. And, in fact, having a period every month can be dangerous. Every time a woman has a period, tissue lining sheds and new cells must grow to replace it. And every time there is cell regrowth there is a new chance for mutations to occur. This leads to an increased risk of cancer and cysts.

It may be healthier (and more natural), then, for women to suppress menstruation (the way pregnancy used to). But because the idea of a natural rhythm is now synonymous with monthly periods, introducing pills with alternative cycles has proven difficult. Pills that allow for four periods a year (like Seasonale, Seasonique, and Yaz) have come on the market. But instead of discussing the medical benefits of fewer periods, they are marketed in a woman-on-the-go sort of way, as a way for women to “take back” their lives by avoiding an inconvenience.

Marketing the pill in this fashion has created push back by women who think this method this pill is all about suppressing “natural” womanhood, but it is a falsely constructed version of womanhood to begin with.

Lauren McGuire interned for Sociological Images in 2010. See more posts from Lauren on social psychology and policing by race and the evolution of Cosmopolitan magazine.

Comments 84

Mordicai &mdash May 6, 2010

This post is one of my favorites. This is absolutely correct. A+

REAvery &mdash May 6, 2010

My sister does something like this. She says it's the best thing she's ever done for herself, except for all the women who feel compelled to tell her she's not a real woman anymore.

I guess all post-menopausal, trans, and otherwise not-menstruating women aren't really women either?

Leslee Beldotti &mdash May 6, 2010

Great article! I figured out a long time ago that I could completely supress my period by skipping the placebo pills entirely.

I was surprised by the negative reactions I got from some of my female friends when I told them that I was skipping my period in this way. As the article stated, they believed that doing so was somehow "unnatural".

The only problem I experienced by taking birth control pills continually was that it significantly reduced my libido.

So I could either eliminate painful menstrual cramps, or I could eliminate my sex drive. THAT was a very tough choice to make!

Tree &mdash May 6, 2010

When you think of the pill, the first image that comes to mind is that iconic little container of pink and white pills that represents one menstrual “cycle.”

maybe in the US, but not everywhere. my pills were yellow and came in a blister pack.

But, speaking from an evolutionary standpoint, there is nothing natural about having a menstrual period every month because it is not natural to limit fertility.

true, that. but it's also not exactly "natural" to ingest synthetic hormones that trick your body into believing it's pregnant.

and, for some of us, all it does is fuck up our immune systems.

the idea that women should suppress menstruation in order to reduce the risk of cancer and cysts is about as sensible as the idea that women should bear children in order to reduce the risk of breast and endometrial cancer.

Renee &mdash May 6, 2010

I would just amend your analysis a bit to note that our ancestors spent a good portion of their reproductive years pregnant OR NURSING (which suppresses ovulation, prevents periods, and does an ok job of contraception, although I wouldn't rely on it.)

Deaf Indian Muslim Anarchist &mdash May 6, 2010

wow. I didnt know that menstrual periods are considered dangerous for our health.

Phoquess &mdash May 6, 2010

The obnoxious thing about the need for monthly periods is that I have to take BC continuously so that I can stay functional when I would ordinarily be useless because of period cramps. So I skip placebos—and then end up needing 15 packs a year instead of 12, because they decided to give me 12 weeks worth of useless pills. (Even Seasonale etc. give you 4 weeks worth—I don't want a period AT ALL!)

Astrid M. &mdash May 6, 2010

Sorry, I fail to see how birth control that causes one to have 4 periods a year is supposed to be more "natural" than having a period 12 times a year.

I was on Depo Provera, the hormone shot, for about 2 years. It's also supposed to cause less periods per year, which sounded very convenient, and is what convinced me to try it. But in actuality, I found my "light spotting" to be pretty much daily for at least a year. I didn't find that convenient in the least! But the real problem was feeling exhausted and depression, which ultimately lead to thoughts of suicide. Sure, the side effects I felt were extreme and very few women experience this. Still, no doctor warned me of the possibility of that happening. I ended up staying on it so long because I thought there was an adjustment period and things would sort themselves out. Might I also add, feeling depressed to the point of suicide killed my sex drive - no sex = 100% effectiveness against pregnancy! )

Anyway, cut to a few years later, I don't use hormonal birth control, but rather an IUD. I personally don't find women using hormonal birth control with all the possible side effects - mood altering, libido altering, increased risk of blood clots, loss of bone density, etc. to be "normal" or acceptable. Let me know when there's a pill on the market for men!

Margilynn &mdash May 6, 2010

Well I would like to counter a rebuttal with the link: http://www.scarleteen.com/article/body/i_being_born_woman_and_suppressed

B &mdash May 6, 2010

I'm guessing that the makers of Seasonale et al also make monthly-period pills as well, right? Well, I doubt they want to market those pills as being less likely to cause cancer than the other pills they sell!

Angel &mdash May 6, 2010

"Our female ancestors spent a good portion of their reproductive years pregnant and not having a period. And, in fact, having a period every month can be dangerous."

"It may be healthier (and more natural), then, for women to suppress menstruation (the way pregnancy used to)."

I do question these comments. Can we without a doubt say that our female ancestors were healthier because of this? To me those comments rely to much on speculation and ignores the possible risks that may have been involved in that suppression. At this point artificial suppression has not been around long enough to know that it poses no long term risks either. Like it or not the women of the world are still the guinea pigs testing that theory out.

C.G. &mdash May 6, 2010

I'm not sure if I should be surprised that no one has mentioned this, as it's surprisingly difficult to bring up. But here goes:

If you're on the pill and you have drastically reduced or eliminated periods, how do you know and react if it fails?

Mila &mdash May 6, 2010

As a young woman with PCOS and in an active sexual relationship, I prefer to have my monthly period, and if I skip one on purpose, I'm very paranoid about being pregnant until I have it.

I have multivarious factors that go in to how I feel about periods. I had my first period when I was 11. By the time I was 13, I was throwing up from pain each time I had my period. But my periods were far from regular. I'd go 3 months inbetween, then 1, then 7, then 2. No rhyme or reason. Just sudden pain and blood everywhere and vomit. Let's just say that I really had a good reason to never want another period again.

Then when I was 16, I managed to find doctors that recognized my symptoms for what they were (PCOS) and put me on the pill. It was such a relief! I actually had an idea of when it was coming. It also reduced the flow and the pain became a 1 compared to the 9 I had been experiencing.

It's 10 years later, and now I'm worried about my fertility. PCOS is rather scary in that department. I pretty much have no idea what to expect. I could get pregnant while on the pill or I may never get pregnant. Also there is a high chance of miscarriages for women with my syndrome. All of this makes me feel that having my period almost every monthis the best way for me to take care of myself and any children that may come along. (I do skip on purpose now and then, vacations and anniversaries and birthdays are good excuses in my book.) I want to know, as soon as I reasonably can, when I become pregnant. As much as I would love to never have a period again, I can't see myself ever managing to try for that.

Rose &mdash May 6, 2010

"And, in fact, having a period every month can be dangerous. Every time a woman has a period, tissue lining sheds and new cells must grow to replace it. And every time there is cell regrowth there is a new chance for mutations to occur. This leads to an increased risk of cancer and cysts."

Heather Leila &mdash May 6, 2010

And associating the pill with a monthly cycle as some concession to the Church - which doesn't give a fuck how you package or construct it anyway? How many pre-Vatican ancient cultures noticed the cycle as monthly, as related to the lunar cycle and all that? Doesn't it seem like the cultural monthly construction comes out of the biological construction? And yes, I know not all women have regular once-a-month cycles, but guess what? Even the moon doesn't have a regular once-a-month cycle.

This post just gets me. We all know having your cycle can suck, can hurt, can embarass. But to say it's more natural not to have it? Because our ancestors would have been pregnant at the moment instead of menstruating?

If we are left on our own, no pregnancy, this IS our natural state.

Md &mdash May 6, 2010

One thing that I would like to bring up is that I do not have regular 28 day periods. They can be anywhere between 25-37 (I used to keep an Excel spreadsheet of the data. yikes!). As a teen, I was told by my doctor, friends, aunties etc etc that I should be on the pill in order to FORCE a 28 day cycle because my natural cycle was "wrong". I've never been on the pill and I continue to have a non-regular period.

I truly belive that my body regulates itself and for example, if I'm stressed or have a cold my period will often be slightly delayed. Seems like my body is smarter than these pills.

Carrie.uk &mdash May 6, 2010

There are many comments flying around, and in the article, about what is natural. I think this whole word needs more thought put into it. Both to what it can be applied to, and its assumed superior status.

Whether something is natural or not is pretty debatable. One might argue that regular cycles are natural, because from a hormonal perspective, if a woman had no pregnancies she would have them continuously. But looking at things from a wider perspective, during evolutionary history few women would be left on their own with no pregnancy (us being group mammals). Thus most women would experience a number of pregnancies and a number of period free years. So which state is more 'natural'?

Secondly, some comments seem to carry the implication that because something is natural, it is desired. I would argue that even if something is 'natural', it is not without-question best for us.

For example the author argues that not having a period every month is more natural and less dangerous, however the 'natural' way to be in that state (pregnancy) carries a number of risks in itself, as far as I am aware. The 'synthetic' method (the pill) of achieving this result also carries health risks, for example increased DVT risk and slight breast cancer risk increase.
On the other hand some commentors are suggesting that having a monthly period is more natural, but there are possible negative health impacts of this also - for example I know a number of women who are mildly anaemic through heavy periods. Some of these take iron supplements because of this, which are of course, not natural but do improve their health.

My point here isn't to do a risk analysis of each state, but just to suggest that there are negative/positive health effects of both 'natural' and 'non-natural' states, and we shouldn't just assume that because one is 'natural', it is best for us or that we SHOULD be doing it.

Lia &mdash May 6, 2010

I am only now reeling to deal with the fact that I have a medical condition that I might have to control with supression BC. It is not a pleasant thing to deal with, because, yes, I do enjoy my periods, and yes, I find it kind of weird to take hormones that fool my body into thinking I'm always pregnant. I also think that it is bizarre that women are supposed to believe that a process that occurs naturally and regularly is "harmful"-- way to make me feel better about my body, guys!

I find the basic premise of this argument kind of flawed-- the words menstruation, menses and period are all tied to the idea that women are supposed to bleed monthly, or with the moon! These are not new words at all.

Bagelsan &mdash May 7, 2010

A lot of people are really missing the point on this one. :p Half the rebuttals so far are blithely using the word "natural" as if it's some kinda trump card, when the post is specifically challenging that assumption. The "natural" state of women has clearly not been established, and the benefit of achieving this "natural" state (if it's possible to achieve at all) is clearly uncertain at best. So enough with the "nuh-UH, periods are natural"-ing, please, it's repetitive.

M. &mdash May 7, 2010

Given the nature of this blog I think it's important to mention that birth control is not always pink. I've been on at least 5 different kinds, none have been pink. This doesn't have anything to do with the subject of this essay but more caution should be used here than anywhere when it comes to statements about what comes into everyone's mind when they hear something.

Anonymous &mdash May 7, 2010

It might be interesting to know that in the UK it is quite common for someone to be on the pill that eliminates the need for periods at all. I, myself, have been on it for over two years and it's a free prescription drug.

I find it odd, that the advert posted is distracting from the fact that it is contraception, like it's all about stopping that irritating period. Is it possible that this makes it look like it's denying or vilifying a natural process?

Fernando &mdash May 7, 2010

The word natural is a tricky thing. We use it all the time but it is essentially empty. There is no such thing as natural. Certainly we evolved to live under certain conditions and our body and behavior will reflect that, but it means nothing.

We have long abandoned the setting that has shaped us in favor of our incredibly "unnatural" modern world. We shouldn't be worrying about what is natural and what isn't. Natural became a word to say that something is inherently good (superior) because it is part of some greater scheme, but in our context none of this makes sense.

April &mdash May 7, 2010

Here's my reply to this blog post: http://thesocietypages.org/socimages/2010/05/06/the-pill-and-the-invention-of-the-monthly-cycle/comment-page-1/#comment-288282

There are a couple of things that I would like to address with this blog. Firstly, just because the pill was created by someone who calls himself a Catholic does not mean that it “was heavily influenced by the Catholic Church”. The official Catholic teaching has been clearly against the use of contraception from the pill’s inception. Pope Paul VI, in Humanae Vitae explained the Church’s opposition to contraception. You can see the Wikipedia article about it here: http://en.wikipedia.org/wiki/Humanae_Vitae

Secondly, there is a difference between not having a period due to pregnancy and breastfeeding, and not having a period due to the hormonal manipulation of our bodies. I find it quite misleading that you mention the dangers of having a monthly period and act as though those dangers are less than the dangers of using contraception, such as the risks of blood clots, heart attack, future infertility, future miscarriages, etc. Furthermore, several studies have confirmed the link between the use of hormonal contraceptives and the especially agressive triple negative breast cancer. This is especially dangerous for women who use the pill prior to their first full-term pregnancy. You can see information about this here: http://www.youtube.com/watch?v=g_JTkqXIPjg

Lastly, I would also like to add that (in case anyone has this assumption) that the options aren’t between having twenty kids, and contracepting. There is a really natural and effective way to space pregnancies called Natural Family Planning, which isn’t just used by Catholics anymore. It’s used by people who are concerned with the harm to ecosystems caused by the number of women using hormonal contraception (http://www.lifesitenews.com/ldn/2009/jan/09011901.html), by people tired of the side effects, and by women who like having control over their bodies themselves by their knowledge of how their bodies work, rather than giving that control over to medical staff and pharmaceutical companies.

Niki &mdash May 11, 2010

Out of what orifice did you pull the idea that it might be more healthy/natural to suppress monthly periods with drugs? As a species we did not skip straight from being pregnant/nursing most of the time to being on the pill. In the hundreds of years between being walking baby factories and pill-poppers, women could avoid pregnancy with condoms and other techniques. And not everyone out there is on the pill today. Those of us who are not pregnant and not on the pill have a periods approximately every month, and there is nothing "harmful" about it. Inconvenient maybe, but I think the risks associated with the pill itself are the greater evils.

BG &mdash May 12, 2010

Interesting, I really didn't know that. However, this post seems to take a negative attitude toward getting one's period. I understand that the situation is different for every menstruating woman, as some experience extreme pain and would probably much rather not have them, but I don't mind them. I feel no desire to suppress my period. But I also wouldn't judge women who don't want to have a period. Women should be free to choose whatever is best for themselves. Still, I think this post could have been a little more objective. I'm sure there are pros and cons to both suppressing the period and having it. Let's not swing to the opposite side of the pendulum and start saying that having periods is the problem.

It's extremely funny to see that the Pill was invented by a Catholic person, especially considering how conservative Catholics are against birth control currently. Just to set the record straight, I support birth control and would use it myself, but only if I was in a sexual relationship.

I also want to agree with Fernando that the word "natural" is meaningless.

Carloing &mdash March 7, 2012

Which inventor was the catholic?

Sara Lin Starred It: 2013-04-02 (Beautiful Belly Edition) | saralinwilde &mdash April 2, 2013

[. ] few words on contraception and menstruation, and how unnatural it really is for women to have their period every month . . . because in nature, [. ]

My Mother either didn’t know what the “PILL” was for… or knew and didn’t tell me | Saffrons Rule &mdash January 4, 2014

[…] THE PILL AND THE INVENTION OF THE MONTHLY Cycle […]

Heather &mdash December 7, 2015

They would be required to present clinical data demonstrating a benefit to claim that in marketing or in the label. To prove benefit like that would require massive clinical trials that would increase costs and time to market.
The FDA and other national regulatory authorities watch that closely on approved drugs and licensed biologics. They don't have the free reign homeopathic magic potions and supplements have.

Trent Boult &mdash December 21, 2020

Zonebao Molecular Sieve is a manufacturer specializes in carbon molecular sieve serial products in Chin Our precept is using our sincerity and perspiration to win your trust and cooperation.

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When did our ancestors switch to a menstrual cycle instead of the estrous cycle? - Biology

Seattle family planning doctor Deborah Oyer routinely asks new female patients, “How often do you want to have your period? Monthly? Every three months? Or not at all?” Until she asks, some don’t know they have a choice. Like every other aspect of reproductive health, menstruation is a fraught topic. A woman who is actively managing her period is in control of her fertility in Judeo Christian folklore, she is cheating Eve’s curse. Even talking about menstruation can violate taboos. Consequently, most of us are astoundingly under-informed about a facet of womanhood that affects anyone who either has a uterus or loves a person who does.

For example, did you know that:

  • Modern Western women have four times as many periods over a lifetime as our hunter gatherer ancestors and triple the number for women just a hundred years ago. In other words, what seems “natural” now is very different from what our bodies have historically supported or have evolved to support.
  • In the 19 th Century there was approximately a five year gap between when females started their periods and age at first marriage now the gap is closer to fifteen years, with many girls starting in grade school.
  • Girls who start early are more likely to have painful cramps and heavy bleeding. can be as severe as early labor and can trigger vomiting or blackouts.
  • Menstrual symptoms cause over 100 million lost work hours annually for American women they are the number one reason young women miss school or work. In the developing world menstruation is a factor in adolescent girls leaving school.
  • A woman can now choose to regulate her periods using either short acting contraceptives like pills or rings or a long acting method like an IUD or injections.
  • Given an option, about one third of women would choose to keep their period the other two thirds would prefer to ditch it.
  • There are no known long term health consequences of menstrual regulation or suppression in healthy women. (which are as effective as sterilization from a contraceptive standpoint) were recently approved by the FDA to decrease menstrual symptoms and endometriosis and are rapidly becoming a first-line treatment for many menstrual problems.
  • A hormonal IUD reduces menstrual bleeding by on average 90% and many women have no period by the end of the first year –yet menstruation and fertility return within a single cycle after removal.
  • Italian researchers found that menstrual symptoms and related absenteeism accounts for approximately 15% of the wage and promotion gap between men and women.

Over the centuries, many religious leaders have taught that women were made for childbearing, and some, known as complementarians, take this position today. Fortunately, few go as far as Reformation father Martin Luther: If a woman grows weary and, at last, dies from childbearing, it matters not. Let her die from bearing she is there to do it. Complementarians are right in one sense: our bodies are optimized to produce the greatest number of surviving offspring, even if it costs us in other dimensions of health or wellbeing. In past centuries this meant a high level of mortality for women and babies. Historically, one woman died for every hundred pregnancies. When that is multiplied by a traditional number of pregnancies per woman, you get a maternal death rate close to ten percent, similar to what it is in Afghanistan today. Globally, half a million women die each year due to complications of pregnancy and childbearing.

Producing babies with big brains is rough, and our bodies work very hard each month to ensure that we have surviving offspring despite the odds. In a sense, each menstrual period is an incident of failed pregnancy. The uterine lining thickens just in case some lucky egg-sperm fusion should come along and attach itself to the endometrium. Even with this month-after-month cycle of preparing for pregnancy, it is now thought that most fertilized eggs fail to implant. From a biological standpoint, gearing up for pregnancy each month is costly, which has made evolutionary biologists curious about the advantages. The evolutionary disadvantages are easier to spot: anemia, for example, and a blood or scent trail that might attract predators.

Menstruation and reproduction are as entangled with culture and religion as they are with each other. The ancient Hebrews justified the pain and trauma of childbirth, along with subjugation of women, through the Eden story. In it, Eve is created from Adam’s rib to be a “helpmeet” to him. Later, God punishes her for eating from the tree of knowledge: I will greatly increase your pains in childbearing with pain you will give birth to children. Your desire will be for your husband, and he will rule over you. (Genesis 3:16) In the Hebrew religion, menstruation was not only physically unclean, it was spiritually unclean, as was childbearing, and a woman was unclean for twice as long when she gave birth to a baby girl as a baby boy. On the other hand, in many cultures and for some women in our culture, menstruation is a point of pride. Childbearing is a form of power, one of the greatest powers in the world, and menstruation is a sign of that power. Onset is accompanied by rituals as solitary as days of isolation or as social as community feasting and dancing.

Given the cultural significance of menstruation, it should come as no surprise that a variety of groups and individuals are uncomfortable with the idea of women choosing or not choosing to have periods. In this regard religious conservatives find themselves in unfamiliar company. Some of their fellow advocates are wary of the medical establishment and instead promote natural living and alternative medicine. Some hate the “medicalization” of women’s bodies and reproductive health and think we should embrace menstruation as part of what it means to be powerful, female and sexual. Some believe that the ovulatory system has other health functions and shouldn’t be messed with. (Until the Population Council developed what is now the Mirena, it was not possible to actively manage menstruation without also suppressing ovulation.) Some have had bad experiences with hormonal contraceptives. Some find a spiritual rhythm and serenity in the monthly cycle. Unfortunately, the cultural or spiritual weight given to menstruation means that matter of fact, pragmatic information can get pushed to the periphery, distorted or even suppressed.

That is unfortunate for women who simply want to manage their lives. It is especially regrettable for millions of girls and women with debilitating cramps, severe bleeding or menstrual migraines. For most of us, how often we menstruate is not some form of cultural advocacy. It is a practical, personal question. Evolutionary programming aside, most of us don’t want to maximize our number of pregnancies. Many of us don’t care particularly about what religious leaders think of “Aunt Flo.” We simply want to take care of ourselves, our sex lives, and our children or future children. We don’t want cramps, bloating, back aches, nausea, fatigue, mood swings or migraines. But we do value our fertility and want to make sure that we can have babies when we feel ready. We are interested in avoiding anemia and endometriosis and plain old monthly malaise, but we are cautious about profit driven medical treatments that affect our reproductive tracts. Some of us also like to dance in leotards, swim in bikinis, race in triathlons, work in military combat zones, backpack in bear country, or wear white in the summer. All of this means that we want accurate, practical information and options when it comes to our periods.

Ironically, when research first began on the Pill in the early 20 th Century, menstrual symptoms like dysmenorrhea (pain) and menorrhagia (heavy bleeding) were front and center in the conversation. Preventing conception itself was so controversial that it was listed as a side effect on an early application for FDA approval. In 1873, at the behest of anti-obscenity crusader Anthony Comstock, the U.S. Congress had passed the Comstock laws which made all contraception illegal. Condoms could be sold only for “feminine hygiene.” Such was the situation when Margaret Sanger’s mother died at age 50 after eighteen pregnancies and eleven live births. Sanger herself was tried for a Comstock violation in 1936. After that, prosecutions dropped away, but thanks in part to advocacy by Catholic leaders and conservative Protestants contraception remained controversial. Feminine hygiene products, on the other hand, flourished, and so it was natural that as contraceptive technologies emerged so did carefully worded conversations about hygiene and menstrual management.

From the beginning, doctors recognized that there was no medical reason for women on the Pill to bleed, but they thought Pills would be more accepted by the public and by Catholic authorities if they mimicked a monthly menstrual cycle. For women who are taking oral contraceptives, monthly bleeding triggered by seven days of placebos isn’t actually menstruation, but rather a response to hormone withdrawal. Real menstruation is evidence of a feedback loop in which a functioning hypothalamus and pituitary signal the ovaries and uterus, causing a follicle to develop and egg to be released into an environment that is ready to receive it. The hormones in most oral contraceptives suppresses this cycle of ovulation. In other words, women who are on the pill to regulate their periods aren’t actually regulating them. They are suppressing them and replacing them with withdrawal bleeding, and benefits of menstrual suppression accrue whether the monthly bleeding occurs or not. For two generations, women using hormonal contraceptives have bled monthly for cultural reasons, most without knowing there were alternatives.

Fortunately we now have other options. No matter how often a woman wants to have periods, monthly, every three months, or not at all, there are state-of-the-art top tier contraceptives that can fit the choice. That is why Dr. Oyer’s question, “How often do you want to have your period?” is a reasonable one for her to ask her patients. If you are female, it is also a reasonable one for you to ask yourself.


Growth Variation in Humans 6

Sara Stinson is a professor at CUNY Queens College. She received her Ph.D. from University of Michigan in 1978. Her focus is on physical and developmental variations among living human populations. She studies environmental influences on growth and the evolution of body size. Her research has been mostly on South American populations, including variation in indigenous South American populations, effects of high altitude hypoxia, and growth of lowland tropical forest populations.

Growth Variation: Biological and Cultural Factors

Variation in size is one of the most obvious ways that humans differ. These differences are also easy to measure and compare across populations, making this a well-studied topic in biology/anthropology. Many factors can contribute to growth variation across and among populations such as genetic factors, nutrition, environmental conditions, social conditions, and cultural conditions.

Genotype can have a strong effect on growth as shown in the next two examples. Our ancestry and previous natural selection pressures on our ancestors affect growth patterns.

The range of the average height for the tallest and shortest populations is less than one foot. The shortest population, the Efe pygmies of central Africa, is less than 5 ft. tall on average. While poor nutrition plays a role, it has been shown that these populations have a reduced number of sites for growth hormone to attach on their cells which would lower the effect the hormone has on them. Smaller body size could have been selected for since it would be advantageous to be small in this hot, humid environment, but no genes that could be attributed to natural selection have been identified.

Another genetic example of growth variation is the difference in males and females. In the US male and female average height is approximately 6 inches different. The height ranges can be represented by two overlapping bell curves. While males tend to be taller, females tend to carry more subcutaneous fat than males, and females carry their weight in different areas than men. These sexually dimorphic tendencies exist in every human population, and are contributed to by hormonal differences during adolescence and puberty.

Environmental Factors:

Most size variation in the world’s populations is attributed to environmental factors.

Socioeconomic Status is one of the major players that can contribute to size variation. Socioeconomic status can limit access to quality health care and nutritious food, while having an increased exposure to disease. Scientists can look at income, education, occupation, and household possessions to determine this status. In almost EVERY study done so far children from high-income families are taller than children from low-income families. This difference is more noticeable in developing countries than in industrial countries. Economic inequality exasperates this phenomenon. Some argue that short stature due to economic status could be attributed to higher levels of stress in low-income families. Low-income is also associated with higher rates of obesity in developing and industrial societies where high-caloric, low-nutrient foods are cheapest.

Ideology and Beliefs have also been shown to influence growth. Families in Niger would rather keep their possessions important for determining rank, instead of selling them for money, because in this culture status is very important. In the US parents may opt out of forcing their children to eat healthy foods in order to maintain a peaceful dinner environment because here an emphasis is placed on having positive family dinners. In Tanzania children from monogamous marriages were taller and thinner than children from polygamous marriages.

Environmental Pollutant (toxicant) exposure has been associated with reduced height. Prenatal exposure to cigarette smoke and/or alcohol shows babies that are born smaller. Children with high blood lead levels have slower prenatal and postnatal growth and delayed puberty. Polychlorinated biphenyls (PCBs) can increase maturation rates in girls. Girls with higher levels of PCBs have earlier menarche, but there is little affect on overall growth patterns.

Recent Trends in growth patterns show that height and weight have increased in populations around the world. Over the last 100 years in Sweden, female height has increased by almost 5 inches and male height by almost 8 inches. This next part is a little unintuitive, but trends show that we are maturing earlier as well as faster. The age of menarche has decreased from 15-16 in the 19 th century to 12-13 years old in most industrialized societies. Increases in leg length are higher than the increase in trunk length. European populations are now on average taller than Americans. While the height of populations in Oaxaca, Mexico has remained the same for 500-3000 years, during the last 30 they got a health center and secular trends have showed up in children’s growth patterns. Recent Mayan immigrants to the US have children that are approximately 4 inches taller. 70% of this height increase is attributed to longer legs.

Why are these trends happening though? The change in the last 150 years has happened too fast for it to be attributed to genetics. The reduction of infectious diseases could be a factor-improvement of world populations overall. Greater gene flow between populations could also be a factor. The increase in body size appears to be slowing and plateauing in affluent countries. A downside to these trends is that an earlier age of menarche has been deemed risk factor for breast cancer, heart disease, and type 2 diabetes. Obesity is becoming an ever-increasing problem around the world. About 67% of US adults are overweight or obese.

Nutrition and Disease throughout the Life Cycle

Parental Growth usually assessed by birth weight can give indications on how an individual will grow. Babies less that 5.5 lbs are considered to have a “low birth weight” which can result from prematurity, slow growth during gestation, genetics, or multiple births. During WWII women in Russia and the Netherlands were under siege from the Germans reducing the amount of food entering the cities. Birth weight decreased in these populations, with 50% of babies in St. Petersburg being born with low birth weight. An increase in maternal nutrition during pregnancy shows an increase in birth weight. However, if a woman has been malnourished her entire life, increasing nutrition during pregnancy is not enough to increase birth weight. Babies can adjust their metabolism to what they (and their mother) are experiencing during pregnancy. So if a woman is normally well nourished, but during pregnancy is malnourished, this cannot only make the baby be smaller, but also change the child’s overall metabolism. Maternal cues to the fetus including placental transfer of nutrients or hormones would be an epigenetic effect. Studies have shown that a women’s birth weight is a strong predictor of her children’s birth weight.

Infancy and Childhood Growth is more important, however, in terms of its affect on body size and health. Disruptions in the growth of children are the main cause of small adult body size. Human milk is relatively low in fat and protein content indicating frequent nursing and slow rates of postnatal growth. Breast-feeding infants is very beneficial for developing infants. Other feeding methods do not provide anti-infective agents that help in the development of the baby’s immune system. These agents include antibodies against specific bacteria and viruses white blood cells and proteins, fats, and carbohydrates that convey antimicrobial action. Bottle-fed infants have higher rates of illness and mortality than breast-fed infants. It can be “argued that breast milk is the nutritionally ideal food for infants because it is the food that has evolved to meet their needs. “ Breast-feeding is associated with lower risk of ear, respiratory and gastrointestinal infections sudden infant death syndrome asthma and reduced risk of obesity and diabetes in the children.

During the first few months of development, infant growth rates are consistent in poor and developed countries. However after the age of 4-6 months the growth rate in infants in disadvantaged circumstances decreases. By two years, there is a substantial different in height. The slowing of growth is referred to as growth faltering. By 5 years old, children in poor countries fall below the 25 th percentile for height. In rural Mali cultures young children are not encouraged to eat, and must fend for themselves. But in rural highland Peru children are given preferential treatment, and in times of food shortage are given food over adults. Growth faltering is not only nutritional but also caused by diseases. Children and infants exposed to pathogens may experience more growth faltering.

What did you think of the Mali cultures?

Adolescent Growth is less affected by environmental factors due to the fact that this period is characterized by slower growth rates. In some environments rapid maturation is necessary due to high mortality rates. Rapid maturation results in smaller adult body sized, but the individuals can reproduce at an earlier age. In these cultures there is a trade off between rapid maturation and small adult stature.

Catch-up Growth is a period of faster growth that follows a disruption. Turkana populations are initially below the 50 th percentile and sometimes lower than the 5 th percentile in height, but when they reach maturation they are on the normal standard. This can be explained by a longer growth period in these populations.

Is small body size an adaptation? It has been argued that when a human is exposed to low-nutrition environments they may cut their losses and remain smaller so that the resources that they have can go father. This would allow for more fit individuals that are smaller than their maximum potential.

Human height variation is a complex outcome of gene and environmental interactions. Narrowing down the cause of height to one factor is impossible, and when looking at height distributions you must take into account genetic history, environment, nutrition during development, social status, and cultural influences.


Evolution May Explain Why Men Are More Likely To Cheat

Studies routinely find that men are more likely to cheat on their partners, commit sexual misconduct, and act recklessly when it comes to sex. Why have men evolved to be more sexually impulsive, and can we learn to change our ways?

Couple getting married. Infidelity continues to be the one of leading causes of divorce. (Getty . [+] Images)

While 20% of men have reported having extramarital sex, only 13% of women report sharing this experience (and much of this behavior, on both sides, likely goes underreported). Women are also double as likely to experience some form of sexual violence over the course of their life. Such reprehensible behaviors may be the products of the evolutionary history behind the male sex drive.

Evolution, biology, and the platitude “boys will be boys” do not excuse poor and inconsiderate decision-making. But there are biological factors (as well as numerous cultural factors) that may make men more likely than women to act upon their sexual impulses. A stronger understanding of the origins behind this gender difference can help us address and prevent such shortcomings as our society continues to change.

For instance, the sexual pursuit area of men’s brains may be up to 2.5 times larger than that of females. Men report masturbating over twice as frequently as women , on average, with their primary motivation being insufficient sex. Upon reaching puberty, men begin to produce 25 times more testosterone (the male sex hormone).

Although this is obviously not true of all men , on average, a male’s brain is, evolutionarily, more primed towards sexual conquest.

The Birds And The Bees

The image of the male as the more promiscuous seems nearly universal in the animal kingdom, although there are some exceptions, such as the female pipefish which actively courts the male.

Toads engaged in intercourse (Getty Images)

The explanation behind the behavior differences of the sexes has been accepted for a long time: since females birth and nurture the children, they must invest more in finding a worthy mate. Males, on the other hand, are incentivized to spread their sperm as far as possible.

Despite popular misconceptions, humans are not the only monogamous creatures, and in fact, the majority of human cultures actually practice polygamy (both polygyny, the practice of having many wives, and polyandry, the practice of having many husbands, are common throughout history). On the other hand, many birds and even our close relatives the gibbons almost always partner for life .

A Muslim Uighur man rests with his two wives and their six children. (Getty images).

Over the course of evolution, our style of social organization has affected our sex lives and thus our anatomy. For us, monogamy is a recent invention-- the earliest human ancestors likely lived similarly to chimpanzees today, in large multi-male, multi-female groups. This organization is the optimal strategy for a species on the move. Meanwhile, primates with one dominant male and many females, like Gorillas or Orangutans, typically have the male defending some piece of valuable territory for his harem.

The Race Of The Sperm

Our ancient, polygamous male ancestors thus had to compete with each other to father the most children. One consequence of this was “sperm competition,” wherein males evolved larger and specifically shaped penises (ours are the largest of all the apes) in order to ensure that their sperm were the ones that made it.

Men also evolved to produce more sperm, leading us to develop relatively large testes. Since the birth of monogamy in humans, however, our testes may have somewhat shrunk, while chimps, still in their harems, have maintained the largest testes of all apes (not surprisingly, the purely monogamous gibbons have the smallest). Nevertheless, our larger testes mean more sperm and a brain more interested in delivering those sperm.

Chimpanzee mother and child. (Getty Images).

Women, in turn, transitioned from the nearly universal in the animal kingdom “estrous cycle” (where a female is perceivably “in heat” for a short period of time) to the “menstrual cycle.” The cycling hormones of the menstrual cycle may make the woman more open to sex regularly (at least compared to the estrous cycle), and it is not obvious to the male when she is fertile.

In doing so, the ancient woman may have provided more frequent sex to her male partner (without him knowing if she is fertile) and thus convinced him into providing resources for her and the children. In other words, some scientists believe menstruation coincided with the birth of monogamy and partnership in child-rearing (or at least alimony). Others even argue that humans evolved to walk on two legs in order for males to carry food in their freed arms to nursing females. Yet others believe monogamy is much more recent, and evolved in order to protect against STDs with the growth of large groups. All these theories, however, remain controversial, even after decades of debate.

Nevertheless, the invention of monogamy (or at least, lifelong, single partnerships) may have led to an "evolutionary dissonance" of sorts: men had evolved for millions of years to seek lots of sex with many partners, while women now expected a partner for life. The introduction of cultural and social norms placed even more constraints on sex. In turn, some men have decided to engage in infidelity, and even sexual misconduct, in order to satisfy their basal desires.

Can Brain Keep Up With Phallus?

Obviously, the phallus was not the only organ to grow over the course of our evolution the even greater growth of our brain has helped to prevent us from acting on our impulses.

However, this vast expansion of our brain, partnered with a narrowing of our hips in order to stand upright, forced human babies to have to be born with exceptionally small brains just to fit through the birth canal. We are the only primate to undergo two-thirds of brain growth in the two decades after birth. This trend, in turn, created the uniquely human period of “adolescence," where our bodies are fully functional, but our brains are not.

Often times, the hormones and sex drive of puberty arise in males before the full development of the decision-making portions of the brain. Partner this testosterone surge with alcohol or drugs, and unfortunate crimes, such as sexual assault or rape, are more likely to ensue. Such teenage recklessness demonstrates the dangers when sex drive overpowers ratiocination.

In other words, it is likely that males have evolved to want more sex than they often get in single partner relationships, while young men can develop their sex drive before their full powers of decision-making. When sexual impulse overruns the more the recently-evolved rational and empathetic portions of the brain, some men can be driven to act on their desires without consideration for others, resulting in adultery and other forms of sexual misconduct.

The male libido (and female acquiescence to it) may be more ancient and hard wired into our brains than our recently evolved "higher intelligence," but that doesn't mean it has to be more powerful.

We have come a long way from our primal ancestors on the African Savannah. Just as the majority of us have evolved to value monogamy, bodily autonomy, and empathy, so too can we teach ourselves to overcome even our most hard-wired sexual impulses.

In order to prepare our children for the complex interactions of the modern world, we must instill in them respect for contracts, like marriage, and for the rights of others, and instruct them on how to think with their brains, evolution’s greatest endowment to us. In doing so, we pass on behaviors that will help future generations thrive, as our ancestors did for us.

Read about an ancient love triangle that changed the face of humanity today here.


The Development of Agriculture

The development of agricultural about 12,000 years ago changed the way humans lived. They switched from nomadic hunter-gatherer lifestyles to permanent settlements and farming.

Social Studies, World History

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Farming is a worldwide industry, and many immigrants carry their agricultural professions with them into their new homes, like this Polish farmer who immigrated to the United States in 1911 and established a dairy farm in Deerfield, Massachusetts.

Photograph by Robert Madden

the art and science of cultivating land for growing crops (farming) or raising livestock (ranching).

plant with a life cycle of no more than one year, and often much less.

grass cultivated as a grain.

type of grain, including wheat.

large settlement with a high population density.

complex way of life that developed as humans began to develop urban settlements.

to encourage the growth of something through work and attention.

the process of adapting wild plants or animals for human use.

very expressive or emotional.

change in heritable traits of a population over time.

land cultivated for crops, livestock, or both.

region extending from the eastern Mediterranean coast through Southwest Asia to the Persian Gulf.

fruit and tree native to Asia.

change to the genetic structure of an organism.

the gathering and collection of crops, including both plants and animals.

person who gets food by using a combination of hunting, fishing, and foraging.

animals raised for sale and profit.

to move from one place or activity to another.

imprecise term for countries in southwestern Asia, sometimes including Egypt.

2000 B.C.E.) last phase of the Stone Age, following the Mesolithic.

having to do with a way of life lacking permanent settlement.

constant or lasting forever.

period of time that occurred before the invention of written records.

likely to change with the seasons.

large community, linked through similarities or relationships.

prehistoric period where human ancestors made and used stone tools, lasting from roughly 2.5 million years ago to 7000 BCE.

movement from one position to another.

most widely grown cereal in the world.

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Agricultural Communities

Agricultural communities developed approximately 10,000 years ago when humans began to domesticate plants and animals. By establishing domesticity, families and larger groups were able to build communities and transition from a nomadic hunter-gatherer lifestyle dependent on foraging and hunting for survival. Select from these resources to teach your students about agricultural communities.

Hunter-Gatherers

Hunter-gatherer cultures forage or hunt food from their environment. Often nomadic, this was the only way of life for humans until about 12,000 years ago when archaeologic studies show evidence of the emergence of agriculture. Human lifestyles began to change as groups formed permanent settlements and tended crops. There are still a few hunter-gatherer peoples today. Explore the lifestyle of hunter-gatherers in your classroom with these resources.

Agriculture

Agriculture is the art and science of cultivating the soil, growing crops and raising livestock.

Domestication

Domestication is the process of adapting wild plants and animals for human use

Doggerland - The Europe That Was

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Related Resources

Agricultural Communities

Agricultural communities developed approximately 10,000 years ago when humans began to domesticate plants and animals. By establishing domesticity, families and larger groups were able to build communities and transition from a nomadic hunter-gatherer lifestyle dependent on foraging and hunting for survival. Select from these resources to teach your students about agricultural communities.

Hunter-Gatherers

Hunter-gatherer cultures forage or hunt food from their environment. Often nomadic, this was the only way of life for humans until about 12,000 years ago when archaeologic studies show evidence of the emergence of agriculture. Human lifestyles began to change as groups formed permanent settlements and tended crops. There are still a few hunter-gatherer peoples today. Explore the lifestyle of hunter-gatherers in your classroom with these resources.

Agriculture

Agriculture is the art and science of cultivating the soil, growing crops and raising livestock.

Domestication

Domestication is the process of adapting wild plants and animals for human use

Doggerland - The Europe That Was

A map showing Doggerland, a region of northwest Europe home to Mesolithic people before sea level rose to inundate this area and create the Europe we are familiar with today.


Ardipithecus ramidus

Click to enlarge image Toggle Caption

Background of discovery

4.4 to 4.2 million years ago

Important fossil discoveries

Hundreds of pieces of fossilised bone were recovered during 1992-1994, all from localities west of the Awash River, in Aramis, Ethiopia. The finds number over 110 specimens and represent about 35 individual members of this species. Most of the remains are dental, but some skull and limb bones were also found. A partial humerus (arm bone) indicates that this species was smaller than the average Australopithecus afarensis.

In 2005, the remains of 9 individuals were recovered from As Duma in northern Ethiopia. The remains mostly consist of teeth and jaw fragments, but also some bones from the hands and feet.

Some specimens discovered earlier in Kanapoi, Lothagam and Tabarin could also belong to this species.

  • ARA-VP-6/1 teeth: This is the holotype for this species. It consists of teeth and jaw bone and was found in Aramis in 1993.
  • ɺrdi' ARA-VP-6/500: A partial skeleton found in 1994, consisting of about 125 pieces, was described and published in 2009. It is the oldest known skeleton of a human ancestor. The individual is believed to be a female and is nicknamed ‘Ardi’. She weighed about 50kg and stood about 120cm tall.The skeleton was in extremely poor condition and it took the team 15 years to excavate, scan, make virtual reconstructions, assemble and then analyse. The results were hugely significant in terms of how we view the evolution of the earliest hominins and the physical appearance of the last common ancestor of humans and chimpanzees. The skeleton does not look much like a chimp or gorilla or have the expected 'transitional' features. Instead, it may well preserve some of the characteristics of the last chimp-human ancestor. Analysis of the skeleton reveals that humans did not evolve from knuckle-walking apes, as was long believed. It also indicates that chimpanzee evolution underwent high degrees of specialisation since diverging from the last common ancestor and thus these apes are poor models for understanding the appearance of this ancestor.

What the name means

The name is derived from the local Afar language. ‘Ardi’ means ‘ground’ or ‘floor’ and ‘pithecus’ is Latinised Greek for ‘ape’. The name ‘ramid’ means ‘root’ in the Afar language.

Distribution

Fossils belonging to this species were found in eastern Africa in the Middle Awash valley, Ethiopia. Additional fossils that may also belong to this species have been collected in northern Kenya.

Relationships with other species

This species position as a direct ancestor of humans is unclear and scientists are still debating where it should be placed relative to our direct line. The discovers think it was ancestral to Australopithecus - it is the only putative hominin in evidence between 5.8 and 4.4 million years ago - but others do not agree. Even if Ardipithecus ramidus is not on our direct line, it must have been closely related to the direct ancestor and probably similar in appearance and adaptation. It also offers new insights into how we evolved from the common ancestor we share with chimps.

This species was originally classified as Australopithecus ramidus in 1994, but was reclassified in 1995 because its discoverers believed it was distinct enough to be placed into a new genus, Ardipithecus.

Key physical features

This species was a facultative biped and stood upright on the ground but could move on all four limbs in trees. Features of the anatomy are extremely primitive.

  • similar in size to modern chimpanzees. The most complete specimen, a female, stood about 120cm tall
  • males were only slightly larger than females
  • the body shape was more ape-like than humans, but differed from living African apes in a number of significant features
  • mix of primitive and derived features suggest this species was able to walk upright on the ground yet efficiently climb trees
  • long powerful arms that were not used for weight-bearing or knuckle-walking as with quadrupedal apes
  • bones in the wrist (particularly the midcarpal joint) provided flexibility and the palm bones were short. These features suggest this species was not a knuckle-walker and that the palms could support the body weight when moving along branches
  • finger bones were long and curving, both features useful for grasping branches
  • upper and lower legs bones (femur and tibia) have features consistent with bipedalism
  • feet were relatively flat and lacked arches, indicating this species could probably not walk or run long distances
  • they had grasping abducted toe characteristic of gorillas and chimps
  • the foot was more rigid than chimpanzees with the bases of the four toe bones oriented to reinforce the forefoot when pushing off. Chimps have a highly flexible midfoot that improves their ability to grasp and climb but are less effective for propulsion when walking on ground
  • has a mix of features useful for both climbing and upright walking and suggests the species still spent significant time in the trees
  • shape of the upper blades (ilium) appear short and broad like Australopithecus afarensis, indicating that the gluteal muscles had been repositioned. This lowered the body's centre of mass so to balance on one leg when walking
  • the lower pelvis is large and the angle of the ischial surface does not face upward as it does in humans and Australopithecus. These are primitive features that suggest this species had massive hindlimb muscles for climbing and did not walk like A. afarensis
  • the sciatic knotch is similar in size and shape to later hominins. This is a derived feature and is not found in chimpanzees
  • much of the dentition is ape-like including relatively large canines and molars
  • tooth enamel thickness is intermediate between that of chimpanzees and Australopithecus
  • canines are less projecting and smaller than those of all other known apes and there is no evidence of honing. The base of the canines in both sexes are similar in size to female chimpanzees and male bonobos, but have shorter crown heights
  • upper canines are shaped like diamonds, rather than the pointed shape seen in African apes, whch is a derived feature shared with Australopithecus afarensis . Lower canines appear to have less derived features.
  • the jaw displayed significant forward projection compared to humans, but less than modern African apes
  • pre-molars have derived features that are more advanced in the human direction
  • canines (non-sharpened and small) and other teeth share features with Orrorin tugenensis
  • skull rests atop the spinal column, indicating this species was bipedal, although it probably walked in a slightly different manner than humans
  • the cranial base is short from front to back, indicating the head balanced on top of the spine
  • the face is small and in a more vertical position than chimpanzees
  • the ridge above the eye socket is unlike that of a chimpanzee

Lifestyle

Culture

There is no evidence for any specific cultural attributes, but they may have used simple tools similar to those used by modern chimpanzees, including:

  • twigs, sticks and other plant materials that were easily shaped or modified. These may have been used for a variety of simple tasks including obtaining food.
  • unmodified stones, that is stones that were not shaped or altered before being used. These tools may have been used to process hard foods such as nuts.

Environment and diet

Associated animal and plant fossils indicate this species lived a in relatively moist and heavily forested woodland. Fossil species include plants such as fig, palm and hackberry and animals like colobine and baboon-like monkeys, kudu, peafowl, bats, shrews, rodents, doves, eagles, owls and parrots.

The species, with its ape-like feet, probably spent considerable time in the trees looking for food and shelter.

Diet may have included nuts, fruit, leaves, tubers, insects and small mammals. They were probably more omnivorous than chimps (based on the size, shape and enamel of the teeth), and fed both in trees and on the ground. The evidence is inconclusive, but studies suggest the front teeth were regularly used for clamping and pulling, possibly reflecting a diet that included large amounts of leaves. Tooth enamel analysis suggests they ate fruit, nuts and leaves. Carbon-isotope studies of teeth show they ate woodland rather than grassland plants.


Why don't humans have mating seasons?

Lets talk first about why many animals do have mating seasons. The reason is usually quite simple: offspring born at certain times of the year have a better chance at survival. For example, deer mate in the fall and give birth in late spring, ensuring they have plenty of food and time to grow before the harsh winter season. Many tropical fish spawn when the rains come at the end of the dry season, providing their offspring with access to shelter and food in the newly flooded forests along the banks of their home rivers.

In species where offspring survival isn't seasonal, breeding seasons don't tend to exist. This holds for many (but not all) tropical species, including all the great apes. And it holds for humans.

So to get to specifics, below are some reasons it doesn't necessarily make sense for humans to have breeding seasons:

A) none of our related species have them, so neither did our ancestors.

B) Humans are fundamentally tropical (having originated in tropical regions), and thus our "native climate" didn't have the harsh winters that a breeding season is often timed to avoid

C) Humans live in groups and use technology, and this insulates us from the variability of our environment, meaning our infants are less vulnerable to external environmental conditions

D) Humans have very long infancies, meaning no matter when they are born they are going to be experiencing a full year's worth of climate variation as a baby.

D is a symptom of not having mating seasons rather than a reason why. Human infancy grew as we rose through the food chain and our tribes became stronger. When you're getting chased by predators all the time, you need a quick infancy to get on the move. Humans instead have deep tribal connections and a village raising a whole child that infancy can be extended.

When all is said and done, (d) seems like the simplest, most likely answer.

Guarantee that teachers have a mating season that coincides with delivery in May

Like all other organisms, our mating strategy is part and parcel of our overall survival strategy.

In our case, we are extreme "K-specialists". We devote a huge amount of investment and resources in our offspring, compared to, say, willows who just scatter their seed to the wind by the millions.

Our females have developped a strategy of concealed ovulation. Current thinking is that by concealing her ovulation and maintaining a perpetual state of potential sexual readiness, the human female makes it difficult for males to know whether her offpring are theirs. The male counter-strategy is to be at hand as often as possible to prevent cuckoldry. Together, this strategy and counter-strategy promote pair-bonding, monogamy and dual parental investment, thus maximising parental investment in offspring.

EDIT: Thanks for /u/ardent-muses (et alia) for correcting the -r/-K screwup.

Aren't humans K-strategists? R-strategists reproduce quickly and in large numbers, devoting more energy to the number of offspring as means of survival rather than devoting energy and resources into fewer offspring. Please correct me if I'm wrong, I'm only a young biology student.

In what species is it easy for the male know wether or not the female is pregnant with his offspring?

And in those species do males leave the mother/off spring if he knows?

There's also the separate theory of losing visual cues as a result of bipedalism and the loss of hair leading to clothing. Many primates signal ovulation through visual cues, and human males have long since lost constant visual access to female genitalia.

While humans as a species do not have a mating season (and we have evolved without one, as per many of the excellent answers in this thread), I think it would be arguable that we do have several pseudo- mating seasons which varies based on culture/region.

The UK Government has collated data based on the number of births and when they occurred. I understand it is a little bit of a stretch, but if we equate the birthday minus 38 weeks as the average copulation date (as 38 weeks is the norm - link) then you get a fairly clear picture.

With an average number of days in each month as approximately 30, you can say that each pregnancy normally takes 8.866 months (or 266 days) between date of copulation and date of birth.

The heatmap shows that the majority of babies are born between September 17 th and October 4. th

If we look at the period that this overlaps with, we can see a spike in sexual activity between 25 th December and 11 th January. Obviously, this is derived data from a loose heatmap, but the point ought to stand on its own merit - humans have predictable times when they are born, making births around certain times more likely than others. You'll also notice from that heatmap a general period of increased birth rate between June 1 st and November 1. st This correlates with sexual activity during the winter period - September 8 th - February 8. th

Note that while the heatmap exaggerates this, the average in the majority of the year is approximately 1813.25 (source: ONS Infant Birth & Mortality CSV from this related document), we see peaks and troughs throughout the year, dipping as low as 1,359 births/day (likely for reasons outside of natural causes), or 1,700 (otherwise), and as high as 1,974 (Birth: Sept 26 th / Est. Copulation: January 3 rd ).

Note that the average copulation date is very much that, and assumes a lot of things (including a normal distribution of woman's periods throughout a month, a reasonable spread across different races & classes, and a whole bunch of other things that I can't easily control for in an internet post). As such, this information is by no means a comprehensive study.

If you want to come up with a synopsis, humans are most sexually active during the Christmas - New Year holiday season, with other (smaller) hot spots throughout the year. It is nowhere near as drastic a trend as in most species with a set mating season, but we certainly appear to have something close to one.