The 10,000 Year Explosion: How Civilization Accelerated Human Evolution - Gregory Cochran, Henry Harpending The basic argument of The 10,000 Year Explosion (10KYE) is two-fold. The first assertion is that biological evolution still affects the human species, which is evident within historic memory. The second half of the argument is that evolution has accelerated since the Agricultural Revolution c. 12,000 years ago. The authors look at four turning points in human development: (1) the displacement of the Neanderthal c. 40,000 years ago by modern humans, (2) the Agricultural Revolutions (more properly, “revolutions” as farming was discovered several times in several places), (3) Indo-European expansion c. 5,000 years ago, and (4) the cognitive development of Ashkenazi Jews in Medieval Europe.

The second half of the argument is essentially one of numbers. Agriculture permitted an enormous increase in population and density. More genes allowed for more mutations, for good or ill. Beyond the absolute numbers, lies another fact: Humans were now living in environments radically different from those their hunting-gathering ancestors wandered in. Selective pressures fell (are falling) on different genes, and better adapted populations expanded at the expense of less well adapted. I think the evidence is becoming quite clear that this part of Cochran and Harpending’s (C/H) argument is certain. The details of why and what adaptations developed are still matters of controversy. The most infamous evidence for this is Old World humans’ resistance to epidemic diseases like small pox. This adaptation New World humans lacked, and they paid a horrific price.* The first part of the authors’ argument is more tendentious, at least in regards to points (1) and (4), so I’ll deal with (2) and (3) first:

Point 2 – the consequences of agriculture:

1. Old World humans developed resistance to a variety of infectious diseases that became common or evolved in the relatively close-packed, sedentary communities of post-farming humanity.

2. Expansion into more northerly latitudes tended to favor lighter skin color. It’s interesting that the genes that activate this trait are different in East Asian populations vs. European ones. A difference that suggests different evolutionary pressures were working on these groups. Another interesting point the authors make is that the European gene (or complex of genes) has had the most visible consequences – Europeans show the greatest variety of hair, eye and skin color.

3. Human skeletons have become more gracile, and skull volume has decreased.

4. The acceleration of genetic mutations has resulted in an abnormally high (compared to other species) rate of miscarriage.

5. A large number of mutations are found in genes that control human cognition and the nervous system. C/H suggest some of these mutations are the results of trade offs between muscle and brain power. Other mutations point to changes in the ear, which may be related to language development.

It’s instructive to read this section in light of my recent perusals of The Origin of Consciousness in the Breakdown of the Bicameral Mind. Jaynes would agree that humans haven’t always thought the same way but it doesn’t require belief in Jaynes’ theories to accept the fact that our ancestors could have thought in profoundly different ways than we do. Finlayson supports the opposite view, apparently – human cognition hasn’t significantly changed in a quarter of a million years (which, I think, is too extreme a position).

6. Farming cultures were always on the edge of starvation since populations expands more rapidly than food supply (the Malthusian trap). This had the interesting consequence that the better off were reproductively more successful than the poor. Thus, if there were any biological basis for their success, the wealthier passed on their genes to future generations while the poors’ were lost. (This, too, flies in the face of Finlayson’s belief that marginal populations are the more successful in evolutionary crises.)

7. As a species, humans became more tractable (i.e., tamed). Aggressive behavior (particularly among males) may have had an evolutionary advantage in a scattered, hunter-gathering economy but in the new agricultural communities, its utility was reduced and could be downright disadvantageous. As a consequence, nicer, less aggressive humans became more successful. We may decry our modern propensity to follow the herd but without it, modern life would be impossible.

Here, C/H make one of their more controversial and, IMO, more specious arguments: That in nonagricultural populations one will find less submissive individuals, indicated by their unwillingness to be enslaved. They point to the absence of Native American slaves in European colonies as evidence for this, ignoring their earlier contention that New World humans couldn’t easily live with Old Worlders because of the disease issue and ignoring the historical record. I think this is a case of carrying biological determinism too far. Biologically there were any number of reasons that Old and New World humans couldn’t mix easily but that one was the uncontrollable aggression of New World captives seems far fetched. Among themselves Native Americans were more than happy to enslave each other, and I’m sure that had they been less susceptible to disease would have been better represented on Spanish haciendas and American plantations.

8. So-called bourgeois virtues – hard work, deferred gratification, property (biologically – securing resources necessary for successful procreation) and selfishness – became advantageous and were pressured for selection.

9. Agriculture selected for cognitive traits that made trade and long-range planning easier.

Here again the authors make another of their ill-supported, poorly integrated claims: Modern-day nonagricultural societies may have an evolutionary disadvantage in adopting and adapting to modern society above and beyond any barriers erected by colonialist policies, racism and corrupt politicians because their brains aren’t as capable of thinking in a “farming” mode as long-established agricultural societies. This is another example, IMO, of biological determinism run amok. You don’t have to invoke biology to understand why so many countries worldwide are still “developing” after centuries of supposed aid, or to explain Western domination of the modern era.

I like point (3). Here’s an example where a biological basis for the observed history has some foundation. About 5,000 years ago, a group of tribes spread out from a common homeland (probably south Russia/Ukraine between the Black and Caspian seas) to overrun earlier tribes from the Atlantic to India. Their dominance is reflected today in the fact that half the planet still speaks languages descended from these Indo-Europeans. What contributed to Indo-European success has confounded historians and archaeologists for years. The authors point out that arguments from technological superiority or social organization falter in the fact that these traits (esp. the technical ones) are easily copied. They might have explained initial success but can’t account for the continued success of Indo-European expansion over the course of several millennia. C/H contend that the secret of their success was their lactose tolerance. Because Indo-Europeans were able to more efficiently utilize their cattle, they had reproductive advantages that drove them on to overwhelm their less efficient neighbors.

It’s an intriguing hypothesis that I find moderately persuasive.

Now we return to points (1) and (4).

Point (1): Around 40,000 BC, a profound change in the material culture of modern humans expanding into the Middle East and Europe took place. This is most spectacularly represented in the cave art of southern France and northern Spain. C/H lay the emergence of these innovations squarely at the feet of the Neanderthal, who contributed genes by mating with incoming moderns.

To begin with, the assertion that our ancestors successfully mated with Neanderthals is far from settled. From my reading, there’s no clear evidence that H. neanderthalensis contributed anything to our genome but the science is still in its infancy and I remain, and the authors should have remained, agnostic on the subject. Or at least provided greater evidence for it. If it becomes obvious that my great-to-the-Nth-degree grandfather Skrag the Hunter was a Neanderthal, I’ll happily accept him at the next family reunion.**

Again, it’s instructive to read Clive Finlayson’s The Humans Who Went Extinct, where he points out that the timing is all wrong for a material-cultural explosion and our encounters with Neanderthals, and that the cave paintings are unique to France and Spain. Nowhere else do we find a culture that expressed itself in the same way. Indeed, the art of the earliest sites is clearly from a different tradition than that of later sites (which are separated by 20 millennia). And – if the preceding weren’t enough – material culture is rarely preserved. We are in no position to make generalizations based on the evidence we have.

The authors’ fourth example of recent evolutionary change is the most sensitive in this day and age: The Ashkenazi Jews of Central Europe evolved measurably greater cognitive abilities reflected in their disproportionate representation in finance and the sciences. This difference from their neighbors arose because of centuries of reproductive isolation and inbreeding (a cultural consequence of Christian anti-Semitism). I don’t find the idea that such isolation may have selected for a particular genetic expression. European Jews were genetically isolated and forced into occupations that Christians wouldn’t or were forbidden to do (i.e., banking) to a much greater extent than outside of Europe. But I’m not convinced that it has a biological basis, or a significant one at any rate. C/H claim that the successful Ashkenazi foetus was selected for skill in mathematics and critical-thinking skills but they base their conclusions on the efficacy of modern IQ testing and a belief in the inheritability of success on those tests – again, propositions that are still contentious and, again, best to remain agnostic about. The truth of their claims may have to wait for a millennia or two – Since the 19th century, the artificial barriers to greater Ashkenazi admixture with Gentiles have come down both in the bedroom and the workplace. If there’s truth in Ashkenazi cognitive superiority and it’s an advantageous mutation, then we can look forward to all of our descendants being just a little bit smarter.

I have wavered between two and three stars for this book. This subject is of immense interest to me and defaults to the “I like” rating unless there’s some serious deficiency in the writing or argument. In the end, I’ve decided to give it 2.5 stars for two reasons: One is that it’s too short. C/H don’t give their arguments proper support and give contrary evidence short shrift, often dismissing it with a snarky, off-hand remark as illustrated in the note below. The second reason is purely an aesthetic one. I hope that it will be a passing trend but this is another mainstream book on science that adopts a faux folksy idiom totally inappropriate to the subject matter and annoying to boot.

This is an interesting book and despite my caveats well worth the time to study. If nothing else, the book points up the fact that we still have an enormous amount to learn about human evolution and its role in our history – about learning who we are, who we were and who we may become.

* C/H make the interesting point that New World humans may have been doubly cursed because not only were they unprepared for infectious diseases but their immune systems were fundamentally weaker than Old Worlders’ since they were descended from a single gene complex, and would explain why the complex urban, manifestly farming civilizations of the Aztecs and Inca were just as vulnerable as the unfortunate Taino of Hispaniola.

** It’s unfortunate, and a serious flaw of the book, that the authors’ typical reply to counter arguments is specious. In the case of Neanderthal introgression, their response is essentially, “Humans will f**k anything”: “As for the idea that people just wouldn’t have wanted to mate with creatures that were so different, we can only say that humans are known to have had sexual congress with vacuum cleaners, inflatable dolls, horses, and the Indus river dolphin. Any port in the storm, as it were” (p. 37).