A Troublesome Inheritance: Genes, Race, and Human History. By NICHOLAS WADE. Penguin Press, 2014, 288 pp. $27.95.
It is hard to disagree with the journalist Nicholas Wade when he writes in his new book, A Troublesome Inheritance, that “human evolution has been recent, copious, and regional.” Modern humans first began dispersing around the world about 50,000 years ago, as small bands of around 150 individuals departed their ancestral homeland in Africa to form new colonies elsewhere. And those settlements eventually sent out pioneers of their own, and so on, for tens of thousands of years. Over time, humans were exposed to intense evolutionary pressures that varied according to each population’s local climate, geography, fauna, and flora.
For example, the ancestors of contemporary East Asians and Caucasians, forced to cope with the long dark winters of the north, evolved pale skin, most likely because this trait enabled the individuals who possessed it to absorb more light and synthesize vitamin D, and thus to survive and reproduce more successfully in dark areas. Other genes found to be modified by natural selection are linked to diet, skeletal and hair structure, fertility, resistance to disease, violent aggression, and general brain function. Many of these variations have evolved within the last 15,000 years and affect specific populations: Tibetans, for instance, are thought to have developed the necessary changes in blood cell regulation required to thrive at high altitudes a mere 3,000 years ago.
The basic biological facts of human evolution are indisputable, and A Troublesome Inheritance is correct to point them out. Wade, however, is interested in more than biology: he is also interested in how biological differences among populations have led to social and political differences across societies and vice versa. Wade argues that it's possible to trace how genetic evolution produced behavioral capacities -- and, by extension, social institutions -- that differ among populations. “The genes of the nervous system,” he writes, “have been under selection for the same reason as the other genes -- to help people adapt to local circumstances. Changes in social behavior
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