Is our genome decaying (see “Genetic Entropy”), and, if so, is this evidence for our genome being “young”?

In the book Genetic Entropy & the Mystery of the Genome the author says that the genome cannot be old because the genome is "decaying". Decay is a very subjective term, but in this case he means that the fitness of humans is going down not up. Is it true that our genome is decaying over time, and that the fitness of humans is decreasing? Here is a quote from the book, that might explain his argument:

Kondrashov, an evolutionist who is an expert on this subject, has advised me that virtually all the human geneticists he knows agree that man is degenerating genetically. The most definitive findings were published in 2010 in the Proceedings of the National Academy of Science by Lynch.4 That paper indicates human fitness is declining at 3-5% per generation.There is really no debate on current human genetic degeneration.

Perhaps this more shines more enlightenment in my question. This idea of human fitness going "down" is my main concern. Essentially, in his book he claims that because we are going "down" (meaning fitness is declining) not "up" (whatever that means) our genome must therefore be young. If I understand the issue correctly, mutations "create new information" by creating different proteins or leading to an abnormal protein products. However, I thought that the force of natural selection should be strong enough to get a rid of those genes that are so and so responsible for our fitness declining.

Sanford, John C., and John R. Baumgardner. Genetic Entropy & the Mystery of the Genome. Waterloo, NY: FMS Publications, 2008. Print.

Feel free to point me to similar questions that may been helpful or are similar to this one.

If I understand the question correctly, you are asking why random mutations (most of the non-silent ones are deleterious) cannot create information and improve the overall fitness of the organism.

This is a common creationist statement, and has been shown to be incorrect in many different ways. The best way this can be shown to be false is by simply applying natural selection.

E. coli has a beneficial mutation rate of $10^{-5}$ per genome-generation (source) and a detrimental mutation rate of $2×10^{-4}$ per genome-generation (source).

Therefore, at first glance, the claim that the "genome is deteriorating" appears plausible. However, natural selection quickly acts on these mutants with deleterious mutations due to their low fitness. Therefore, the deleterious mutations are removed from the gene pool and are replaced with their beneficial counterparts instead.

If we define "information" as beneficial adaptations to the environment, random mutations themselves do not directly create the information. It is the application of natural selection that allows the fitness of the organism to increase despite the presence of random mutations.

Regarding the reference to Lynch, actually reading this paper is illuminating ( What Lynch is saying with regards to degeneration is that he and others feel that modern technological advances may relax selection pressures, thus allowing the survival and reproduction of many who would otherwise be selected against, increasing the rate of mildly deleterious mutations in the human population.

Sandford willfully misreads this in order to inject his creationist/intelligent design mythology (Man's creation by god, the fall, no evolution, but rather decay from god's perfection, etc). However, this is definitively NOT what Lynch and other biologists are suggesting. Decay is a loaded word. The genome is constantly changing from generation to generation on an individual basis. Selection simply eliminates overtly deleterious mutations.

Lynch is suggesting a sort-of technological doomsday, where human success at subverting selection ultimately lead to an unsustainable mutational burden and the collapse/extinct of humanity. Differences in selection pressure affect what genomes are propagated onward. Previously deleterious mutations that can be survived in our current environment are seen some malign decay, but this is how selection works. As the environment changes (including technological changes), selection pressures changes. If selection pressures revert, such persons will once again be selected against. An overly dramatic shift in selection pressure (such as collapse of society, or other forms of massive environmental change) could indeed kill us off, but this is true of any species and is in no way unique to humans.

A small addition to what March Ho has mentioned in their answer.

Fitness is not absolute; it is dependent on the present environment. Fitness has no meaning when the selection factor is not defined.

You can consider a commonplace example: Can you, by just looking at an individual say how fit they are (of course I am not talking about those who are clearly ill, obese or malnutritioned)? Unless you assess their performance in a task you cannot really say how fit they are. Same goes with evolution.

Now consider another hypothetical example. You would be aware of the fact that the sickle cell trait (mutant haemoglobin) provides immunity against malaria. If your task is some kind of physical exercise then obviously the sickle cell trait is deleterious. However, if there is a malaria pandemic then the sickle cell trait would provide a great survival advantage and therefore these individuals would be deemed fit under these conditions.

It is to be understood that evolution does not work towards "improvisation" of species. Just because we assume that a certain trait is advantageous for an organism, it is not necessary that it would evolve. Have a look at this post.

Well, you've already mentioned Alexei Kondrashov. Here's his talk (in russian unfortunately):

To summarize it:

Yes, that decay is happening and at a pretty catastrophic rate. As of 2012, he estimated the rate of IQ decay (and fitness decay is somewhere close) to be within the range of 1% and 10% per generation. The former is ok according to him, cause "in 100 generations we'll surely be swept away by a nuclear war between big-endians and little-endians". The latter will be unfortunate, cause in 10 generations we'll "fall prey to our own stupidity". He speaks of stupidity because our brain is the most transcriptionally complex structure in our organism, thus it suffers from genetic damage sooner than anything else.

(It's worth noting here that AFAIK, one of Kondrashov's children has Down syndrome; another one, Fedor, is a remarkable geneticist as well, focused on epistasis.)

Those estimations are supported by the following molecular data: no matter the age of the mother, she gives 15 new single-nucleotide mutations on average to her offspring. Father gives about 10 mutations per each year of his life after reaching puberty, historically 70 on average. Out of those mutations most are neutral or silent (due to genetic code degeneracy), but on average ~1 out of 70 leads to a change in aminoacid sequence of some protein, usually harmful.

Here are 2 papers: decay of cognitive indicators of children with parent's age:

Another link from Kondrashov: drosophila simulation of middle-class neighborhood (MCN) population, where each family has exactly 2 children, son and daughter, and no natural selection pressure is applied: such population rapidly deteriorates with fitness in wilderness decreasing by 2% per generation: Kondrashov says that after several generations you can hear the difference between MCN drosophila and wild-type - wild-type is much more noisy and active.

He also mentions that frequency of autism, diagnosed in the US has increased 5-fold since 1950.

Watch the video: Barry Schuler: An introduction to genomics (January 2022).