Comments on: Study Suggests Increased Rate of Human Adaptive Evolution

By: Renata

Renata — Sat, 12 Jan 2008 11:59:02 +0000

Great news! you article was accepted for our Natural Science Carnival! Visit the Carnival here and don't forget to comment, link back, spread the word!

By: Greg Laden

Greg Laden — Sun, 16 Dec 2007 10:41:19 +0000

Henry: You need to demonstrate that the differential reproduction is linked to a heritable trait.

By: henry harpending

henry harpending — Sun, 16 Dec 2007 09:37:42 +0000

Oops, sorry, I misread you about Clark–you spoke of his “social darwinism” rather than his “eugenics.”I don’t see anything unusual or remarkable about what he says. Greg you remember very well the cottage industry of the 1970s and 1980s showing that wealthy people had higher fitness here, there, and everywhere. How could that process fail to have genetic consequences? It must have, and Clark finally is laying out a hypothesis about what those consequences were.Can you propose a scenario in which the differential reproduction would have had no evolutionary effect?Henry

By: Henry Harpending

Henry Harpending — Sat, 15 Dec 2007 23:31:13 +0000

Everyone has their undies in a bunch about our remarks about evolutionary rate. One audience that was not the least perturbed by these remarks has been agricultural geneticists, who know all about evolutionary rates. They all just said “of course”.The so-called “breeders’ equation” is a workhorse of evolutionary biology as well as quantitative genetics. It is taught in AgSci 101. It says the response to selection is the product of the additive heritability and the selective differential. So if the parents are on average 1/10 of a standard deviation higher than the rest of the population on trait x, and if the heritability were 40% (which is a good generic guess for almost anything anyone has ever measured) then the change per generation would be .04 standard deviations. After 20 generations, say 500 years, the change would be .8 standard deviations. This really does mean that a whole lot of evolution can happen real fast over time scales of millenia.What on earth is controversial about this??And what are Greg Clark’s eugenics proposals?Henry

By: Colugo

Colugo — Sat, 15 Dec 2007 21:54:58 +0000

Greg, I don’t think these kinds of implications (which I do not agree with) are just in the comments to the press. It’s in the paper itself.Consider this passage:”In our view, the rapid cultural evolution during the Late Pleistocene created vastly more opportunities for further genetic change, not fewer, as new avenues emerged for communication, social interactions, and creativity.”…in light of the history of differential population sizes of Africa, Europe, and Asia and differential adoption of agriculture.But on the subject of statements to the press:http://tinyurl.com/2n37dt“”We are more different genetically from people living 5000 years ago than they were from Neanderthals,” said Professor Hawks. “In the last 40,000 years humans have changed as much as they did in the previous 2 million years. …Dr Hawks said the value of most genetic changes, including many in the brain, remained a mystery. Some could involve personality, or help our brains be “more perceptive”.”

By: Greg Laden

Greg Laden — Sat, 15 Dec 2007 20:21:57 +0000

(Oh, and henry, I assume people were not making the connection between your paper and Clark is because we think there might be some hope for the geneticists, but we know clark, and his neo-social darwinism is a crock of shit. Right?

By: Greg Laden

Greg Laden — Sat, 15 Dec 2007 20:14:57 +0000

Henry! Great to hear from you.I’m sure the Middle Ages, as well as WW II and the Plague and lots of other things have left their mark on Europe. Many, many people who live in Europe today came to Europe after these events (depending) and there’s been a lot of other gene flow. Many people from Europe, who’s ancestry was affected by these events, have gone elsewhere to bring their accelerated genetic novelty to places like Australia and Peru and so on.I think there are two BIG errors being made here. One is making up shit. Just because one finds (possible) statistical evidence of increased evolution (and I think you probably have that right) does not mean that any idea that happens to fall out of someone’s head (or other body part) is worthy of exposing to the press as an obvious conclusion. You should know better than to assume that the press will not take and run with whatever you feed them. Go test your hypotheses and then come back with something interesting.The second big mistake is equating the concept of bounded, fairly static races with an expanding dynamically changing population with increasing rather than decreasing degrees of interaction. I’m not sure who’s been saying that (as supported by your paper) but it’s been around.

By: Colugo

Colugo — Sat, 15 Dec 2007 19:20:03 +0000

Also, Dr. Harpending, perhaps you could discuss how recent adaptive human evolution relates to phenomena such as D4 dopamine receptor allelic variation,http://www.pnas.org/cgi/content/full/99/1/10changes in the size and shape of the cranial vault since the Upper Paleolithic, cultural change, and reproductive strategy.

By: Colugo

Colugo — Sat, 15 Dec 2007 18:43:00 +0000

The relationship of the PNAS paper to Clark’s thesis (as well as some others) did occur to me. I, too, have been surprised that there has been so little discussion of the implications of the paper for recent human evolution in cognitive abilities and temperament. Perhaps you could elaborate on this topic for us.

By: Danniel Soares

Danniel Soares — Fri, 14 Dec 2007 11:17:05 +0000

I haven't read the paper and not even most of the bloggin around it yet, but I have a few doubts. Is really safe to assume that this acceleration that looks adaptive is really adaptive?It's a sort of common sense that evolution is slowing down for humans due to technology, agriculture, medicine and etc, but that's actually valid only for adaptive evolution, not neutral, which would actually speed up (in absolute numbers, even though the rates would still pretty much constant). Natural selection not only gradually ceases to filter or benefit mutations as drastically as before, but at the same time artificial changes in the environment allow the population to grow larger than previously possible (more food available, more group protection, more protection from climate, etc), further increasing the total genetic variability.The funny thing is that natural selection is not actually something that can ever speed up evolution in a certain way, but only reduces the relative speed from the maximum potential of evolution, which would be the mutation rate undisturbed. That's why neutral evolution is faster than natural selection.Even when natural selection is really fast, when some selective factor actively kills most of the population that lacks some adaptive trait, then unavoidably it will cause a bottleneck effect, a huge difference in relative genetic frequencies, that is not a product of selection per se, that is, most of the evolution that happened was a only a byproduct of natural selection, but not adaptive in itself.So I think that it's unavoidable to conclude that the distinction between exceptionally rapid positive selection and neutral evolution is reasonably expected to be really blurry, since both are essentially approximations of the full mutation rate potential. Can we really discern it from statistics alone, without pointing how the specific genes differ adaptively between each other?The closest thing that was done in the blogosphere was to point those old examples of lactose tolerance and similar things. But it think that it is not something that settles the whole thing, allows us to accept that populations today differ more adaptively from each other than H. sapiens from 5 000 years ago differed from H. neanderthalensis (if I correctly recall the statement), it's just an example of a few that things that we know that happened.I think that statistics alone can be very tricky under this specific scenario, where, intuitively, the selective pressures are reasonably expected to do decrease. To me seems that, despite of the increase of genetic variability that arises as raw material for potential NS, the potential for actual NS is reasonably rare in our species.No, that's not some anthropocentrist humans-aren't-just-other-animal type of argument - we're the most generalist animal species on the Earth. Human's most important adaptation is a specialization in being the ultimate generalist.Does not appeals much to me the idea that people that were a bit more genetically potentially stronger, or even more intelligent, would have had more children and grandchildren than the others. So I think that, despite of increased variation, it would most likely be things that arose from mutations and just were not harmful enough to be eliminated by NS, not traits that were significantly promoted by NS in detriment of older versions.I think that the immunologic variation would be the more likely targets of actual selection, since vaccines and things like that are very recent and restricted, and since large populations are also a fertile terrain for epidemics. And some other few uninteresting stuff, things that wouldn't make much of a great news report, less interesting than those things of lactose tolerance and the different susceptibility to alcoholic beverage (which has something to do with body size also, if I'm not mistaken. At least for women, that's the proposed mechanism, I think.)And by the way. It was (and still is, sometimes) commonly said that human populations differ more within each other than between each other, even today. I think this statement has or had some empirical basis, rather than being theoretical alone (since intuitively one would more likely expect the opposite). So, that's wrong, or both affirmations don't necessarily contradict each other? We may differ more from each other (or was it from people of 5 000 years ago?) than people from 5 000 years ago differed from neanderthals, and yet we have more differences within populations than between populations?