Monday, August 31, 2009

Before the Dawn

Humans and chimpanzees are the only (current) patrilocal primates. (That is, the males stay put and the females join a male-centred family group.) Humans and chimpanzees are the only primates where the males raid the territories of other groups. Defending territory gives advantages in fathering offspring, so natural selection works in its favour. Hence the raiding logic of patrilocality.

Archaeological and anthropological evidence indicates that human hunter-gatherers are about as murderous as chimpanzees. How murderous is that? If the C20th had had the same rate of war death as hunter-gatherers do, the total number of war dead in the C20th would have been two billion. As for the “myth” of cannibalism, our genetic structure incorporates quite old genetic protection against diseases from cannibalism.

Progress! Humans have become much less violent. One sign of which is that the gap in size between human males and females has shrunk.

The startling calculation above is from P.152 of Before the Dawn: Recovering the Lost History of Our Ancestors, a splendid, and splendidly readable, examination of what genetics combined with archaeology and anthropology can tell us about our origins.

Human males find it easier to cooperate than do males of our chimpanzee cousins, since humans pair bond. Chimp males are in constant competition with all the other males in the group for the group’s females. “Free love” does not mean group happiness! (No economist would be greatly surprised that being in the public domain does not lead to better treatment or less conflict—they would predict worse treatment and more conflict.)

The greater ability to cooperate gave advantages that fed into the selection processes. The evolution of religion makes sense as a means of protecting against the free-loaders who are so destructive of social groups.

Human nature does change, but only very slowly.

Cooperation within groups often was selected for by advantages it gave in competition between groups. The ability to form dialects makes in group and out group membership easier to identify. When archaeologists talk about one culture replacing another in the archaeological record, that replacement was, almost certainly, not a nice process. Rousseauvian fantasies about noble savages do not survive the interrogation of science.

Nor do related fantasies about private property being the source of all social ills—trade gave us a reason to cooperate beyond kin groups.

I was particularly struck by the evidence that, within the Fertile Crescent, sedentism (permanent settlement) preceded the development of agriculture. (The pattern elsewhere seems to have been the other way around.)

The author, a science journalist for the New York Times, is very good at explaining the science clearly and well. Including the increasing evidence that there are notable genetic difference between human populations, including based on continent-groupings (also known as racial groups).

He does, however, seems to have not quite thought through the slowness with which farming was adopted. In discussing the Yanomamo people of the Amazon—a group of cheerful and charming killers—he mentions it only takes them about three hours a day of effort to feed themselves. The much harder work (and higher risk of disease and nutritional problems) of farming is naturally not attractive to them. Farming seems mainly to have spread through spread of farmers—its main advantage being it can support a lot more people.

Genetic studies also through a lot of light on history. For example, the Anglo-Saxon invaders of England clearly intermarried a lot. The basic population of the British Isles is divided between Celts and Anglo-Saxon-Celt hybrids. (Romans and Normans were too few to leave much genetic traces.)

The rate of faithfulness in wives in England over the centuries seems to have been quite high—only about 1% of the sons in each generation of one study extending back to the C14th seem to have had different fathers. So surnames can be quite good indicators of common ancestry. As for the fruits of conquest—there are estimated to be 16 million men living who are descendants of Genghis Khan. Have 500 wives and concubines and then lots of sons who have lots of sons (one had 40 acknowledged sons) and it can mount up pretty quickly. Of course, as Peter Turchin points out, a fast-breeding elite can be a major problem for an imperial system because of the intense competition it sets up among powerholders.

A very enjoyable, informative and well-written book.

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