Are Human Beings Genetically Degenerating?

The claim has been made multiple times that human beings are undergoing some sort of net genetic degeneration.

It’s a little complicated as something to measure, because there are so many confounding variables, but given that the claim is made, it should probably be either supported with evidence or withdrawn.

(let’s leave aside the ‘genetic entropy’ claims of Sanford, and just look at evidence of what’s going on with the human genome as a whole)

I think there some common myths about modern medicine keeping alive people with genetic defects that would have killed them a couple of generations ago leading to net genetic degeneration, but my suspicion is that these are ‘just so stories’ that are superficially plausible to some but not supported by evidence. (Happy to be shown to be wrong if that’s what the evidence says.)

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It’s not exactly the same thing, but there’s direct evidence (e.g. in Jaleal S. Sanjak et al. PNAS 2018;115:151-156) that in developed countries, alleles associated with intelligence are being selected against.

That is not currently a standard in the PS forum. We have whole threads devoted to falsehood, active right now.

If you are asking for specific case studies or human genetics to support the specific claim that you typed, then you will probably come up empty. But I think the onus is on you here. A change in selection pressure will lead to changes in allele frequencies over time, whether or not the selection is positive or negative, whether or not it is sexual selection, and whether or not the lineage in question is our own. This is a very basic tenet of population genetics in evolutionary theory. IMO it’s not reasonable to ask for evidence that relaxation of selection will lead to mutation accumulation in a specific species, because we know this quite robustly in general. It’s an expected outcome of a change in selection, and simply a specific case of that (relaxed negative selection leading to increased mutation load.) It’s the basis of Lynch’s papers discussed in another thread. It is the basis of the entire area of inquiry into genetic load and mutation load. See a recent example paper below.

This is far, far from a “just so story” and I would say it’s the opposite: relaxed selection is known to increase mutation load, and any argument to the contrary will sound at the outset like special pleading.

https://www.cell.com/cell/fulltext/S0092-8674(19)30632-4

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It sounds nothing short of insane. It’s like saying if you reduce gravity you can jump higher. It can’t be denied by a thinking person.

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I’m pretty sure I’ve degenerated quite extensively this year…

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In the US, I can believe that after this year. :laughing:

When I read Sanford’s book a couple years ago, I remember looking up average lifespan of indigenous populations today - ones that don’t get medical care and such. They were typically in the 60’s range. That directly conflicted with Sanford’s ages of patriarchs graph (which had problems anyway).

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It does, but to be fair, the context is a series of “conversations” that are in fact insane. About a fourth of the forum is currently devoted to madness.

That’s why I suggest we might be seeing some special pleading, maybe due to a somewhat understandable stance toward humans as something other than (or somehow more than) a sexually reproducing diploid animal species. Once that stance/bias is removed, a person should be able to see the basic logic and biology behind mutation load and selection.

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“Degenerating” has a negative connotation. As a layman, I don’t know what the distinction is between degeneration (or mutational load) and genetic entropy.

They both seem to depend on a premise that at some point the human genome was better. By what measure is the human genome deteriorating? Fitness seems like the measure of genome quality.

But fitness is generally dependent on context. If the context has changed, and the genome has changed, the genome has degenerated with respect to the old context but has improved with respect to the context, hasn’t it? (Assuming some selection has occurred).

Or is it some measure of absolute fitness. Perhaps a decrease in the rate of population growth is the sign of degeneration? From that standpoint a little degeneration might be a good thing.

To a conservative, everything was better in the past. To a progressive, everything is better now. Okay, I exaggerate just a tad.

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Hi, these are all great questions and points that you raise. Individually and even in subpopulations, the fitness of a particular genotype (or mutation) can be context-dependent. Mutation load refers to the whole shebang, including deleterious mutations that are bad in any context and fitness-reducing mutations that (in any or all contexts) sneak out from under selection (due to drift or to changes in selection pressure or direction).

Re “genetic entropy,” I think one lesson to learn from this thread is that it is nonsense, indeed madness, to talk about mutations (good, bad, ugly) in a population without talking about selection (positive, negative, sexual) and drift. It is not only mistaken, but madness, to suggest that relaxed selection will have no influence on mutation accumulation, because that is the same as asserting that selection has no influence on genomes at all.

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Sanford deals with all of this.

Anyway, if it’s so obvious…why isn’t it considered a major health problem? And why were some denying it? Or did I misunderstand your statement @glipsnort?

Comments on Sanford and Carter respond to PS participants - #130 by glipsnort

Given Sanford’s track record in population genetics, it is unlikely that he deals with it well.

By whom? It’s considered a long-term risk by at least some evolutionary biologists. There’s currently no ethically acceptable solution and it’s not going to cause major problems for some time, so there’s no particular hurry.

That comment says (accurately) that I think Genetic Entropy is nonsense. That has nothing to do with the effects of relaxed selection on numerous human traits.

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Lots of great points and thoughts here so far, thank you.

“Genetically changing” is uncontroversial, perhaps “becoming more genetically diverse”? But I agree, “degenerating” puts both a direction and a value on it, which makes it a social rather than a scientific question.

More later: thumb typing on a phone at a cafe prior to a motorcycle ride in the hills. More scope for complex thoughts when I’m back in front of a keyboard.

It’s also madness to do so without using math.

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