Sex, Murder, and the Meaning of Life

The easy version of evolutionary psychology treats us as clumsy cavemen, running outdated programs that misfire in the modern world. Kenrick pushes hard against that caricature. His central concept is what he calls deep rationality: the idea that behaviors which look irrational on the surface are often exquisitely well-tuned to the ancestral problems they evolved to solve. The apparent stupidity is in our expectations, not in the behavior.

Take conspicuous consumption — the sports car, the oversized watch, the willingness to spend a month's salary on a signal nobody strictly needs. A standard economist might call this waste. Kenrick, drawing on the logic of costly signaling that biologists use to explain the peacock's tail, sees something else. An expensive, useless display is credible precisely because it is expensive and useless: only someone with resources to spare can afford it. In his experiments, men primed to think about attracting a partner became measurably more willing to spend and show off, while women shifted toward displays of a different kind. The spending isn't a glitch. It's an ancient courtship device wearing modern clothes.

Kenrick proposes that inside each of us sits a set of what he calls subselves — distinct functional systems, each built to handle one of the recurring problems our ancestors faced. There is a subself for self-protection, one for avoiding disease, one for making friends and holding status, one for finding a mate, one for keeping a mate, one for caring for kin. They do not usually operate at once. The situation you're in acts like a switch, bringing one to the front while the others wait offstage.

This is not a metaphor stretched for effect; it makes concrete predictions. When people are made to feel afraid, their judgments about strangers shift in specific ways — they become more attentive to out-group men, more prone to see anger in ambiguous faces. When people are made to think about romance, their risk tolerance, spending, and even creativity change, and they change differently for men and women. Kenrick and his colleagues ran versions of these studies for years, and the pattern held: the same person will give measurably different answers depending on which subself is at the wheel.

Here Kenrick makes his boldest move, and it's where the book stops being a tour of dark impulses and becomes an argument about how everything human gets built. He borrows from complexity theory — the study of how simple rules, repeated among many interacting agents, generate patterns nobody designed. Ant colonies build elaborate structures with no architect; each ant follows a handful of local rules, and the cathedral emerges from below. Kenrick's claim is that human society works the same way. Simple, selfish mental mechanisms, interacting across millions of people, throw off staggering complexity that no individual intended.

The love a parent feels for a child is, at the mechanical level, a kin-caring subself doing what it evolved to do: protect the carriers of shared genes. But scale that up, weave it through families and generations, and you get the whole institution of family life, with its loyalties, its art, its self-sacrifice that no gene-counting logic would predict on its own. The selfish part is still there at the base. What emerges on top of it is genuinely generous, and genuinely new.

The book ends more or less where it began, with Kenrick himself — no longer the expelled teenager rehearsing revenge, but a scientist and, in his own account, a devoted father to two sons born twenty-six years apart. The homicidal fantasies never fully vanished; he simply came to understand them as one voice in a crowded committee, not the whole man. That self-understanding is the quiet argument underneath all the provocation in the title. We are not improved by pretending the beast isn't there. We are improved by knowing what it is for.