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Comment by roceasta | Hacker News Reader

>Our rapidly growing species has only accumulated mutations that don't cause us to die

Hygiene, nutrition and medicine (all good things!) also cause us to remain alive where previously natural selection would not have favoured those bearing too great a mutational load.

I doubt that existing mutations have been fully 'tested'. We know that the majority of mutations are harmful and that the brain is far from fully-developed prior to birth, for instance. Being complex there are many genes which control its development and it seems plausible that the result could be sub-optimal without obvious signs of disease or disability. Other things being equal, we could be slower, less resilient, less fertile, etc, than our 18th century forebears.

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I don't think you can remove a discussion about changes in allele frequencies from environments. Thus, making 'other things being equal' is not a reasonable premise from which to discuss evolution.

I do see the argument you are espousing but I would only suggest that you consider the broader context of what happens when new species arise. I suspect you care more about the elimination of alleles (which is surprisingly hard to do), but this is a good example for why I disagree:

One possibility for speciation is the creation of a new niche (lets say a new type of tree grows on an island, its seeds having been carried there by an unusual current). Here, organisms might have increased reproductive opportunities over their neighbors by exploiting this new tree. In time, one could imagine organisms that live in the new tree, like microbes, could acquire enough new features to constitute a new species.

Consider the case where organisms from the original population become unable to grow on the new tree. If the new species is also unable to grow in the original environment, how can we say either is more or less resilient?

That's a pretty subtle case but I don't think it's relevant to the issue of human evolution for at least two reasons:

(1) humans have universal intelligence which gives us the ability to adapt to any environment, (2) human evolution is now swamped by the evolution of memes, not genes. We now decide what to do (including whether to speciate or not)

A more realistic analogy from the animal kingdom would be something like the case of farmed salmon which within a very few generations are less healthy than wild salmon. Also the famous 'mouse utopia' experiment. Both situations where the environment has been artificially manipulated by (human) ideas, just as our present environment is. Mutational loading is one explanation for the results.

So have you considered the issue of mutational load: what's the greatest load we can sustain and what's its present level? Is it responsible, for example, for the declining birth rates in the West or is the explanation for that purely sociological?

I would like to know the answers. However I presume that we'll start by using CRISPR or similar tech to eliminate known genetic diseases like Huntington's and Tay-Sachs. From that precedent should follow the identification and elimination of new and more silent genetic abnormalities. Which is reassuring.

I guess I would need to see an analysis of whether there's been any change in human allele frequencies. I suspect there hasn't.

But to your example, one issue with the farmed fish is that they now constitute a closed gene pool - we can easily explain their decreased fitness with the likely rise of harmful alleles.

With the explosion of population, I don't see much relationship between the salmon and humans.

Thanks. I should read up a bit. Can you link to any decent info or discussion about allele frequencies?

Incidentally, I'll be starting a PhD in a human genetics laboratory, but I don't have a lot of experience with this kind of literature.

This seems like a reasonably accessible (college-biology level) discussion of what evolution would look like in the human gene pool:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2933187/

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EDIT:

I suspect you'll need a university library to access this, but Dr. Pardis Sabeti is well known in this area and also an amazing person - she played a big role in the molecular biology work that underlay the US response to the Ebola crisis. She wrote a review that explains the tools we currently have to ascertain human evolution:

https://www.ncbi.nlm.nih.gov/pubmed/16778047

A recent study that peripherally relates to our discussion came up on my facebook feed:

https://hms.harvard.edu/news/recession-proof

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