Fast Evolution

Jonathan Haidt

Chronicle of Higher EducationThe Chronicle Review — August 29, 2010


[1] The Human Genome Project failed to deliver what it promised—a code book in which we could identify the genes responsible for many diseases. But the reason for this failure is itself a major discovery: The genome is far more dynamic and variable than we thought. Gene activity varies within each person, across the life span, and in response to changing environments. Genes vary at high levels across people, ethnic groups, and eras. This is big news, and I predict that it's going to rock many boats, in many academic departments.


[2] When I was in graduate school in the 1990s, the prevailing view was that evolution was so slow that there could be no meaningful genetic differences among human groups. The genetic "blueprint" was assumed to have been finalized during the Pleistocene era, the two million years during which our ancestors lived as relatively egalitarian bands of hunter-gatherers. Modern humans all draw cards from the same deck, the same population of genes, except for some trivial variations related to adaptations for cold weather (such as lighter skin and smaller noses).


[3] But now that we can examine partial genetic maps from thousands of people around the world, the old view is crumbling. Genetic evolution is not slow, and it certainly did not stop around 50,000 years ago, when people began leaving Africa and filling every continent save Antarctica. In fact, it now appears that the human diaspora greatly increased the pace of genetic change. When people exposed themselves to new climates, pathogens, diets, technologies, and social structures, they exposed their genes to new selection pressures. You don't need 50 millennia to get big changes. Some Russian fox breeders created what was essentially a new species of tame, doglike foxes in just 30 generations.


[4] Over the next 10 years, therefore, we'll be hearing less about the Pleistocene and more about the Holocene— the 12,000 years since the beginning of agriculture. We've accepted findings that some ethnic groups adapted during the Holocene to digest milk as adults or to breathe more easily at high altitudes. But what will happen when findings come in about personality traits? Nearly all traits are heritable, and some traits surely paid off more handsomely in commercial cultures than in agricultural ones, or on peaceful islands than on raid-prone steppes. Such findings will be among the greatest threats to political correctness ever to emerge from the natural sciences.


[5] The good news is that because evolution is so fast we'll stop talking about continent-wide "races." We'll be looking at smaller groups that shared sustained selection pressures for dozens of generations or more. Also, the differences across groups are sure to be small when compared with the large variations found within every group. And finally, any recently selected traits were selected because they were strengths in their original contexts, so future talk about genetic variation might be productively assimilated into our current discourse about diversity, rather than forcing us to replay The Bell Curve controversies of the 1990s. But whichever way it goes, we'll be talking about fast evolution for the rest of the decade.


The 10,000 Year Explosion: How Civilization Accelerated Human Evolution

Gregory Cochran and Henry Harpending

Basic Books, 2009 ― Excerpts from Chapter Three


[1] Favorable mutations are rare, and many of those that do occur are lost by chance. In the small human populations of the Old Stone Age, establishing such mutations typically took hundreds of thousands of years. It's not that it took that long for favorable mutations to spread— the problem was generating them in the first place.


[2] But as human population sizes increased, particularly with the advent of agriculture, favorable mutations occurred more and more often. Sixty thousand years ago, before the expansion out of Africa, there were something like a quarter of a million modern humans. By the Bronze Age, 3,000 years ago, that number was roughly 60 million. Favorable mutations that had previously occurred every 100,000 years or so were now showing up every 400 years.


[3] One might think that it would take much longer for a favorable mutation to spread through such a large population than it would for one to spread through a population as small as the one that existed in the Old Stone Age. But since the frequency of an advantageous allele increases exponentially with time in a well-mixed population, rather like the flu, it takes only twice as long to spread through a population of 100 million as it does to spread through a population of 10,000.


[4] Agriculture imposed a new way of life (new diets, new diseases, new societies, new benefits to long-term planning) to which humans, with their long history as foragers, were poorly adapted. At the same time it led to a vast population expansion that greatly increased the production of adaptive mutations. So agriculture created many new problems, but it created even more new solutions. Earlier innovations had also helped to increase population size and thus had speeded up human evolution, but agriculture had a far greater effect and is in a class of its own.


[5] Naturally, increased population size had a similar impact on the generation of new ideas. All else equal, a large population will produce many more new ideas than a small population, and new ideas can spread rapidly even in large populations. In Guns, Germs, and Steel, Jared Diamond observed:

"A larger population means more potential inventors, more competing societies, more innovations available to adopt— and more pressure to adopt and retain innovations, because societies failing to do well will be eliminated by competing societies." [p.407]


[6] We take this observation a step further: There are also more genetic innovations in that larger population. This is a new picture of recent human evolution. It implies that humans have changed not just culturally, but genetically, over the course of recorded history, and that we must allow for such changes when we try to understand historical events. The implications of this contention are vast: If correct, it means that peoples in different parts of the world have changed in varying ways, since they adopted different forms of agriculture at different times— or in some cases not at all.


[7] Since genetic change wasn't uniform, discrete populations came to differ genetically from one another, and sometimes those genetic differences conferred competitive advantages. We believe that such genetic advantages have played a role in migrations and population expansions— and thus are important in explaining the current distribution of languages and peoples. In fact, history looks more and more like a science fiction novel in which mutants repeatedly arise and displace normal humans— sometimes quietly, simply by surviving, sometimes as a conquering horde.



When the Ice Age ended around 10,000 BC, the world became warmer and wetter, and the climate became more stable. Carbon dioxide levels increased, which increased plant productivity. The stage for agriculture was now set— and this time the actors were ready as well.


[9] Although there had been other interglacial periods in the past, early humans had never developed agriculture then. We suspect that increases in intelligence made agriculture possible, but the route may have been indirect. For example, the invention of better weapons and hunting techniques, combined with other technologies that let humans make better use of plant foods, could have led to lower numbers, or even extinction, of key game animals— which would have eliminated an alternative to farming.


[10] Farming appeared first in the Fertile Crescent of Southwest Asia. By 9500 BC, we see the first signs of domesticated plants: first wheat and barley, then legumes such as peas and lentils.' From there farming spread in all directions, showing up in Egypt and western India by 7000 BC and gradually moving into Europe and India. Around 7000 BC, rice and foxtail millet were domesticated in China. Animals were domesticated on a similar timeline, with the Middle East in the lead. Goats were tamed around 10,000 BC in Iran, sheep about 1,000 years later in Iraq. Both the taurine cattle we're familiar with in the. Middle East and the humped zebu cattle in India were domesticated around 6000 BC. . .


[11] Farming, which produces 10 to 100 times more calories per acre than foraging, carried this trend further. Over the period from 10,000 BC to AD 1, the world population increased approximately a hundredfold (estimates range from 40 to 170 times). That growth in itself transformed society— sometimes, quantity has a quality all its own. And as we have pointed out, this larger population was itself an important factor in evolution.


[12] The advent of agriculture changed life in many ways, not all of them obvious. It vastly increased food production, but the nutritional quality of the food was worse than it had been among hunter-gatherers. It did not materially increase the average standard of living for long, since population growth easily caught up with improvements in food production. Moreover, higher population density, and close association with domesticated animals greatly increased the prevalence of infectious disease.


[13] The sedentary lifestyle of farming allowed a vast elaboration of material culture. Food, shelter, and artifacts no longer had to be portable. Births could be spaced closer together, since mothers didn't have to continually carry small children. Food was now storable, unlike the typical products of foraging, and storable food could be stolen. For the first time, humans could begin to accumulate wealth. This allowed for nonproductive elites, which had been impossible among hunter-gatherers. We emphasize that these elites were not formed in response to some societal need: They took over because they could.


[14] Combined with sedentism, these developments eventually led to the birth of governments, which limited local violence. Presumably, governments did this because it let them extract more resources from their subjects, the same reason that farmers castrate bulls. Since societies were generally Malthusian, with population growth limited by decreasing agriculture production per person at higher human density, limits on interpersonal violence ultimately led to a situation in which a higher fraction of the population died of infectious disease or starvation. . .



[15] Most preexisting genetic variation must have taken the form of a few neutral variants of each gene— variants that are not significantly different from each other. They may well do something, but the neutral alleles all do the same thing. We doubt if many of those neutral genes turned out to be the solution for the problems faced by the future farmers of Eurasia. More likely, preexisting functional variation mattered more. 


[16] For example, there is a gene whose ancestral form helps people to conserve salt. Since humans spent most of their history in hot climates, this variant was generally useful. A high frequency of this ancestral allele among African Americans probably plays a role in their increased risk of high blood pressure today. In tropical Africa, in fact, almost everyone has the ancestral version of the gene. In Eurasia, a null variant (one that does nothing at all) becomes more and more common as one moves north. Perhaps the gene's action of promoting salt conservation becomes harmful—by causing higher blood pressure—in cooler areas, where people sweat less and lose less salt. 


[17] Significantly, the null allele is the same in both Europe and eastern Asia— which suggests that it originated in Africa and is ancient. If it had separate European and Asian origins, then we would expect to see different versions in the two regions, just as different broken pigment genes lead to light skin in the two regions.


[18]The most reasonable explanation for this dud salt-conservation gene is that parts of Africa (before the expansion out of Africa) were cool enough that salt retention was not a major concern, so that in these regions an inactive form of the gene was in fact advantageous. This might have happened in Ethiopia during glacial periods, considering that the climate on the Ethiopian plateau is moderate even today. If so, the null allele would represent preexisting adaptive variation caused by environmental variations inside Africa rather than neutral variation. Such internal variation inside Africa must have helped prepare humans for environments outside Africa. . .


[19] Therefore, new mutations must have played a major role in the evolutionary response to agriculture— and as luck would have it, there was a vast increase in the supply of those mutations just around this time because of the population increase associated with agriculture. We're not saying that the advent of agriculture somehow called forth mutations from the vasty deep that fitted people to the new order of things. Mutations are random, and as always, the overwhelming majority of them had neutral or negative effects. But more mutations occurred in large populations, some of them beneficial. Increased population size increased the supply of beneficial mutations just as buying many lottery tickets increases your chance of winning the prize.


[20] By the beginnings of recorded history some 5,000 years ago, new adaptive mutations were coming into existence at a tremendous rate, roughly 100 times more rapidly than in the Pleistocene. This means that recent human evolution differs qualitatively from typical artificial selection acting on domesticated animals. . .



Individual versus Group in Natural Selection:

Does natural selection drive evolution at levels higher than selfish genes and fertile individuals?

Steve Mirsky

Scientific American ― December 18, 2008


[1] Want to start a brawl at an evolution conference? Just bring up the concept of group selection: the idea that one mixed bag of individuals can be “selected” as a group over other heterogeneous groups from the same species. Biologists who would not hesitate to form a group themselves to combat creationism or intelligent design might suddenly start a pie fight to defend the principle that “it’s every man for himself.”


[2] Yet Charles Darwin himself argued for group selection. He postulated that moral men might not do any better than immoral men but that tribes of moral men would certainly “have an immense advantage” over fractious bands of pirates. By the 1960s, however, selection at the group level was on the outs. Influential theorist George Williams acknowledged that although group selection might be possible, in real life “group-related adaptations do not, in fact, exist.”


[3] Richard Dawkins of the University of Cambridge, whose writings have reached millions, maintains that selection might not even reach such a high level of biological organization as the individual organism. Instead, he claims, selection operates on genes—the individual is the embodiment of the selection of thousands of selfish genes, each trying to perpetuate itself.


[4] In the past few decades, however, group selection has made a quiet comeback among evolutionary theorists. E. O. Wilson of Harvard University and David Sloan Wilson of Binghamton University are trying to give group selection full respectability. They are rebranding it as multilevel selection theory: selection takes place on multiple levels simultaneously. And how do you figure the sum of those selections in any real-world circumstance? "We simply have to examine situations on a case-by-case basis," Sloan Wilson says.


[5] But the Wilsons did offer some guidelines in the Quarterly Review of Biology. “Adaptation at any level,” they write, “requires a process of natural selection at the same level, and tends to be undermined by natural selection at lower levels” . . .


[6] Perhaps the biggest change that group selection brings to evolutionary theory is its implication for so-called kin selection. What looks like group selection, some theorists argue, can actually be understood as genetic relatedness. Evolutionist J.B.S. Haldane pithily explained kin selection: “I would lay down my life for two brothers or eight cousins.” Turning that argument on its head, the Wilsons assert that kin selection is a special case of group selection. “The importance of kinship,” they note, “is that it increases genetic variation among groups.” The individuals within any one group are much more like one another and much less like the individuals in any other group. And that diversity between groups presents clearer choices for group selection. Kinship thus accentuates the importance of selection at the group level as compared with individual selection within the group.


[7] The Wilsons think evolutionists must embrace multilevel selection to do fruitful research in sociobiology—“the study of social behavior from a biological perspective.” When doing so, other investigators can keep in mind the Wilsons’ handy rule of thumb: “Selfishness beats altruism within groups. Altruistic groups beat selfish groups. Every time.”