Sarah Hrdy argues that if human babies were to survive in a world of scarce resources, they would need to be cared for, not only by their mothers but also by siblings, aunts, fathers, friends-and, with any luck, grandmothers. Out of this complicated and contingent form of childrearing, says Hrdy, came the human capacity for understanding ....

Testosterone is a familiar villain, a ready culprit for everything from stock market crashes to the overrepresentation of men in prisons. But your testosterone level doesn’t actually predict your appetite for risk, sex drive, or athletic prowess. It isn’t the biological essence of manliness—in fact, it isn’t even a male sex hormone. So ....