Natalie Angier reviews primatologist Sarah Blaffer Hrdy's new book:

Most biologists would concur that humans have evolved the need for shared child care, but Dr. Hrdy takes it a step further, arguing that our status as cooperative breeders, rather than our exceptionally complex brains, helps explain many aspects of our temperament. Our relative pacifism, for example, or the expectation that we can fly from New York to Los Angeles without fear of personal dismemberment. Chimpanzees are pretty smart, but were you to board an airplane filled with chimpanzees, you "would be lucky to disembark with all 10 fingers and toes still attached," Dr. Hrdy writes.

Jonah Lehrer is impressed:

I'm just so charmed by the hypothesis that human morality - this system of behaviors so often attributed to the Ten Commandments, Kant, etc. - might actually be rooted in the cries and smiles of infants. Babies, in this sense, are the glue that keeps us together - they are so charming that we're nice to each other (or at least we don't hurt each other) for their sake. Religion may have helped codify morality - and one shouldn't underestimate the importance of turning our vague instincts into an explicit set of laws - but our moral emotions existed long before Moses got those stone tablets on Mt. Sinai.

(Photo: a baby in Iraq by Roslan Rahman/AFP/Getty.)

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