Evolutionary psychology Human evolution

“Grandmother” thesis in human evolution takes a hit

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The “grandmother” thesis is that the reason our ancestors didn’t kill granny was that she helped out. (And then somehow religion got involved, and …) An actual study showed that “The hazard of death for Dogon children was twofold higher if the resident paternal grandmother was alive rather than dead. This finding may reflect the frailty of elderly grandmothers who become net consumers rather than net producers in this resource-poor society.”

Oh, and so did the comparison between a human group and co-operatively breeding animals:

It “did not take” a village to raise a child.

In animals that breed cooperatively, adult individuals will sometimes delay reproduction to act as helpers at the nest who raise young that are not their genetic offspring. It has been proposed that humans are also a cooperatively breeding species because older daughters, grandmothers, and other kin and nonkin may provide significant childcare. Through a prospective cohort study of children’s (n = 1,700) growth and survival in the Dogon of Mali, I show that cooperative breeding theory is a poor fit to the family dynamics of this population. Rather than helping each other, siblings competed for resources, producing a tradeoff between the number of maternal siblings and growth and survival. It did not take a village to raise a child; children fared the same in nuclear as in extended families. Of critical importance was the degree of polygyny, which created conflicts associated with asymmetries in genetic relatedness. The risk of death was higher and the rate of growth was slower in polygynous than monogamous families. The hazard of death for Dogon children was twofold higher if the resident paternal grandmother was alive rather than dead. This finding may reflect the frailty of elderly grandmothers who become net consumers rather than net producers in this resource-poor society. Mothers were of overwhelming importance for child survival and could not be substituted by any category of kin or nonkin. The idea of cooperative breeding taken from animal studies is a poor fit to the complexity and diversity of kin interactions in humans.

See B. I. Strassmann, “Cooperation and competition in a cliff-dwelling people” (PNAS Early Edition, 2011/06/13)

Essentially, people who live together in a poor and threatened society are always making harsh, conscious choices between co-operation and withdrawal, and no aspect of the process can be compared to “what animals do.”

Hat tip Dave Coppedge.

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