Down the Millennia (2019)

Book Review from the November 2019 issue of the Socialist Standard

Who We Are and How We Got Here by David Reich (Oxford University Press. £10.99.)

The first ancient human genomes, involving analysis of DNA, were only published in 2010. But since then ancient DNA has had a revolutionary impact on the study of the past, revealing many surprises in what is known about human evolution. Here David Reich, who has played a leading role in such research, describes the state of the art. We cannot summarise the book’s contents here, just focus on some of the main points made.

An important issue which arises is the extent of large-scale migration over the millennia and the consequent mixing of peoples: ‘Most of today’s populations are not exclusive descendants of the populations that lived in the same locations ten thousand years ago.’ Most DNA among Japanese people is inherited from farmers who migrated from the East Asian mainland and mixed with local hunter-gatherers. Everyone in India today is a mix, in varying proportions, of West Eurasian ancestry on the one hand, and East and South Asian ancestry on the other. Mixture often involved men who exercised power and women from a subordinate population; thus Thomas Jefferson, third president of the US, had six children with his slave Sally Hemmings. For biological reasons, men can have far more offspring than women, and one man at the time of the Mongol Empire (maybe Genghis Khan himself) had millions of direct male-line descendants. European men made a far greater contribution to the genetic make-up of African Americans than European women. These are examples of ‘sex-asymmetric population mixture’.

The study of ancient DNA has even more to say about inequality. Around five thousand years ago, the Yamnaya culture spread from the eastern European steppe over northern Europe and central Asia. With wheeled vehicles, domesticated animals to pull them and the use of bronze, they were able to displace local people, and the powerful males among them could gain access to large numbers of women and so pass on their Y chromosomes to many subsequent generations. This did not apply to all men, only to a limited number, which implies a lot of social stratification.

Reich also confronts the question of race, and to what extent notions of ancestry overlap with race. Some people have objected to research along the lines sketched above, on the grounds that it just reinforces supposed racial ideas and categories. He is emphatic that race and ancestry are not the same, yet accepts ‘the possibility of substantial average differences in biological traits across populations’, which would include skin colour, height and the ability to breathe easily at high altitudes. It is hard to see how anyone could object to statements such as this, but claims that some genetic variations are more common in people with more years of education need a great deal more support in order to ascertain the role of other possibly relevant factors.

But all in all, a fascinating and informative, but fairly challenging read.

Paul Bennett