Family Ties

From Michele Pridmore-Brown's review of Robin Dunbar's How Many Friends Does One Person Need? Dunbar’s Number and Other Evolutionary Quirks:

In May 1846, a year and a half before gold was discovered at Sutter’s Mill, several extended families and quite a few unattached males headed with their caravans from Illinois to California. Due to poor organization, some bad advice, and a huge dose of bad luck, by November the group had foundered in the deep snows of the Sierra Nevada. They came to a halt at what is now known as Donner Pass, and, in an iconic if unpleasant moment in California’s history, they sat out winter in makeshift tents buried in snow, the group dwindling as survivors resorted to cannibalism to avert starvation.

From an evolutionary point of view, what makes the story interesting is not the cannibalism — which, in the annals of anthropology, is relatively banal — but who survived and who did not. Of the 87 pioneers, only 46 came over the pass alive in February and March of the next year. Their story, then, represents a case study of what might be termed catastrophic natural selection. It turns out that, contrary to lay Darwinist expectations, it was not the virile young but those who were embedded in families who had the best odds of survival. The unattached young men, presumably fuller of vigor and capable of withstanding more physical hardship than the others, fared worst, worse even than the older folk and the children.

For Robin Dunbar, an evolutionary biologist cum anthropologist, stories such as this one highlight how human kin networks aid survival — and, therefore, why people may take great pains to manufacture kin, via godparents for instance, or marriage, or by obscuring or playing up paternity. He points to another earlier case of extreme selection: of the Mayflower colonists who set foot on the American mainland in 1620, 53 of 103 died in the first New England winter. Here, too, mortality was disproportionately high among the unattached.