I’ve just finished reading The 10,000 Year Explosion: How Civilization Accelerated Human Evolution by Gregory Cochran and Henry Harpending. It got me muttering “What’s their evidence for that?”, “What about …”. Often the authors would address my concerns in the next page or two, sometimes not.
The book got me angry and it got me thinking. Altogether a good read. It is a nice complement to Jared Diamond’s Guns, Germs and Steel. Basically the two books are the nurture/nature or the environment vs genes debate carried over into the destines of whole populations.
If you google either of the names of the authors of The 10,000 Year Explosion, Google’s auto-complete feature will add “racist” to either name. This gives you some idea of what many people think of their work.
Cochran and Harpending’s hypothesis goes something like this:
Human Evolution is accelerating and has been over the last 10,000 years due to the development of agriculture.
The west won because they had better genes, specifically genes for intelligence and hard work, genes for selfishness and for self-denial, genes for living in hierarchical societies, genes for a strong immune system and genes for better digesting wheat and milk.
The west (western Eurasia) gained greater genetic diversity in part from mating with Neanderthal and in part from being able to maintain expanding population (due to agriculture). This greater diversity resulted in more genetic mutations for evolution to work on.
The environment of an agricultural society resulted in those with the above gene variations (intelligence, hard work, submission to hierarchy etc.) having more kids survive to adulthood. This gave westerners the traits needed to take over the world and spread their genes further.
Here’s a few of the points that had me muttering.
Cochran and Harpending state a high correlation between length of time the ancestors of a people have been practicing agriculture and the current economic prosperity of their descendants.
In this as in many other points, I found the book very Eurocentric, or west
The people of the New Guinea highlands have been practicing agriculture for 9000 years. (compare this to ~10,000 years for the middle eastern ancestors of Europeans, ~9500 years in China). The New Guineans also have admixture from an archaic hominin population (Denisovian) to enrich the genetic diversity available for selection. The difference between them and the Europeans seems to be that the New Guinea highlanders did not develop large states to limit inter village violence. Cochran and Harpending don’t address this difference, genes for submission to hierarchy must have developed after the hierarchies. Why didn’t state hierarchies develop in New Guinea?
Jared Diamond is very familiar with the New Guinea highlands and attributes the lack of development of state societies in this area, to the lack of a any local wild cereal plants or large mammals to domesticate.
A cultural explosion or big bang is often stated to have taken place in southern Europe 40,000 years ago. Is this real, or a sampling bias of what has survived and where we choose to look?
Rock art in Australia is hard to pin dates to but some of it is at least as old as that from Europe. The Bradshaw/Gwion Gwion cave paintings in the Kimberly in north west Australia possibly date to 20,000 years and are the equal of any thing in Europe. The Nawarla Gabarnmang are spectacular and have recently been dated to 28,000 years. The world’s oldest known maps are engraved on rocks in Australia. Trade networks were established across the continent. See this great ABC documentary First Footprints. (resource intensive site but has excerpts , or link to DVD purchase)
In general Jared Diamond has a wider knowledge of non-European examples and an explanation for differences in population development based on geography and environment ahead of human biology. Cochran and Harpending explain all in terms of genetic differences.
Culture and environment can have huge effects on some of the outcomes they discuss, just as culture can effect gene frequency. They use the example several times of considering who does the best work in science. Their answer is Europeans since 1600 and Ashkenazi (European) Jews since 1800 and pretty much no one else is or was (e.g. Classical Greece) capable of top class science because they lack the right genes.
But who (if anyone) does the science has a huge cultural component. Over the last 100 years there has been a huge change in women’s participation in science. Obviously (due to the speed of change) this has been driven by cultural change, not genetic change. Although I suspect Cochran and Harpending would argue that the lack of women at the very top science is due to a somewhat higher average for these skills in men resulting in large difference in the numbers of men vs women with the very top skills in science. Of course this would ignore the experience of these women, or the results of this study.
The 10,000 Year Explosion was published in 2009 just before the high quality (4e9 base pairs) sequencing of the Neanderthal genome. Comparisons of this genome with the human genome back up a lot of what Cochran and Harpending say about gene intro-mission from Neanderthal to non-Africans providing a rich source of genetic variation for evolution to work on.
One point they miss on is they presume people will be angered or ashamed by the implication they have Neanderthal ancestry. Judging by the discussion on the 23andme.com Neanderthal ancestry forum (sorry only available to 23andme members), people are extraordinarily proud of their Neanderthal ancestry. On the forum people are competing to report the largest percentage of Neanderthal genetic heritage and collecting anecdotal data on IQ versus Neanderthal percentage.
All these arguments are based on the premise that populations are sufficiently genetically isolated for different environments (mainly cultural) to exert sufficient selection pressure to result in genetically distinct populations. Numbers and equations are given for gene transfer based on models of how far people move to find a breeding partner.
How does this compare with work on modeling the age of the most recent common ancestor (MRCA) in both a regional and global sense? The most recent common ancestor is the most recent individual from whom all people in a group are directly descended. The global human MRCA has been calculated as living as recently as between 2,000 and 4,000 years ago. C&H concept of genetically isolated populations seems more intuitive than this recent a date for our common ancestor. The two ideas might not be incompatible due to the way gene transfer works down generations. After 9 generations (225 years) there is a quite likely that a 9th generation descendant contains no genes from a particular ancestor (one of 2^9 = 512) in the 1st generation.
I’d like to produce a simulation that demonstrates gene transfer, maybe much like a game of life simulation. As the model ran you could see colours blend across a landscape as genes move about through the generations. I’ll have to read the original papers to get a better understanding of the underlying models that produce these results.
The book definitely sets out to challenge the idea that today we are all born equal in terms of our genetic heritage. People descended from long generations of farmers are lucky enough to have inherited genes that are more suited to the modern world those same descendants have created. For those descended from Ashkenazi Jews, just like in the fairy tales there inheritance comes at a price. In this group increased genetic diseases are the price paid for an increase in IQ.
It also raises the very interesting idea that relatively recent historic and prehistoric people were different in behaviour to modern people due to differences in genetics.
I’ve ranted (very selectively) about the parts of the book that got to me. Actually its a book with very bold and audacious ideas that are scientific in the sense they could be proved wrong by new evidence. But I think we’re going to have to get use to the idea that population differences aren’t just skin deep and that human evolution is still in full swing.