Several years ago, researchers shared pictures of past political candidates with a group of children and asked those children to pick which person from each pair they'd prefer to lead them on a hypothetical boat trip. Despite having never seen the faces before, nor knowing they ran for office, the children chose the picture of the winning candidate 71 percent of the time.

That's one of the many cases dissected by Robert Sapolsky in his new book, Behave: The Biology of Humans at Our Best and Worst (Penguin). His point is not that politically chosen leaders are inherently qualified, but that humans are inherently biased, and "our conscious cognitions play catch-up to make our decision seem careful and wise."

Using an interdisciplinary approach that encompasses hormone research in East African baboons (which he's observed every summer for the past 30 years) as well as the neuroscience literature he's taught and written at Stanford, Sapolsky takes a stab at explaining the environmental, genetic, and endocrinological catalysts for human behaviors.

Why, for instance, are teenagers so moody? Because their amygdalae mature faster than their pre-frontal cortexes, and the latter plays a crucial role in regulating the emotional volatility of the former. Their bodies, meanwhile, have reached reproductive maturity, so their brains are experiencing a flood of powerful hormones. And they are surrounded by their peers, who are—to resort to layman's terms—every bit as nuts.

If you prefer neuroscience books that tell you we can use our scientific understanding to fix the world, Behave has a less triumphalist message: that we are lucky to be as civilized as we are. But if you want a better handle on why people are so often violent or prone to acting like robots when marching under a flag, Sapolsky's descriptivism provides a sensible explanation for a nonsensical world.