Hearts and brains. Mind and body. We are quite sure that our thoughts take place in our heads. But what about our emotions? Sometimes we locate them in our hearts, sometimes vaguely in our bodies.

But Stephen Pinker in his terrific 1997 book How the Mind Works explains that most of our moods and bodily reactions take place in the mind. He describes them as “modules” in a computer-like brain, sensation-generating programs that have evolved to keep us alive and reproducing. I’ll highlight a few of Pinker’s explanations of emotions and sensations that are anchored fully and partly in our heads.

Disgust and Sex Two strong emotions, disgust and lust, are products of evolution going back millions of years.

“Disgust is a universal human emotion,” Pinker writes (Kindle location 7865). Its universality is a sign of how thoroughly we are programmed to resist eating animal parts that might contain infectious microorganisms or other toxins. Humans are disgusted by the smell, the sight, or the even idea of eating most animals and animal parts. “The nondisgusting animal parts are the exception.…Many Americans eat only the skeletal muscle of cattle, chicken, swine, and a few fish” (7903). Every other animal is a source of contamination. We won’t drink a beverage stirred with a flyswatter, even if the flyswatter is brand new. We “find a sterilized cockroach every bit as revolting as one fresh from the cupboard.…People won’t eat soup if it is served in a brand-new bedpan….You can’t pay most people to eat fudge baked in the shape of dog feces.”

Such reactions make no rational sense. With rare exceptions, food today is safe. But just try to eat soup from a new bedpan and feel how loudly your bad-food alarm starts blaring, still set to several million years ago.

As for sex, we think we know exactly what its purpose is, one that we share with almost all living things. But here’s Pinker.

Why is there sex to begin with?…Why don’t women give virgin birth to daughters who are clones of themselves instead of wasting half their pregnancies on sons who lack the machinery to make grandchildren and are nothing but sperm donors? Why do people and other organisms swap out half their genes for the genes of another member of the species, generating variety in their offspring for variety’s sake? It’s not to evolve faster, because organisms are selected for fitness in the present. It’s not to adapt to environmental change, because a random change in an already adapted organism is more likely to be for the worse than for the better….The best theory…is that sex is a defense against parasites and pathogens (disease-causing microorganisms). …[Your body’s defenses against germs evolve, but the germ’s tricks for evading those defenses evolve much faster.] Sexual reproduction is a way of changing the locks once a generation. By swapping half the genes out for a different half, an organism gives its offspring a head start in the race against local germs. (9577)

To most people, the evolutionary function of disgust makes some sense. But the idea that sex too plays a role in our resisting disease boggles the mind. The sensation itself is no reliable guide to its evolutionary function, according to Pinker.

Happiness Another important emotional experience has thin roots in evolution but has held a place in human culture and vocabulary for at least a couple of thousand years. But it too, understood scientifically, is not what we expect. This is happiness.

Pinker writes that it might seem at first that happiness serves as an incentive to spur us on towards those conditions that are biologically good for us. These conditions include being “healthy, well-fed, comfortable, safe, prosperous, knowledgeable, respected, non-celibate, and loved” (8097). Set these as your steps towards happiness and you will become an evolutionarily successful human specimen. This certainly has been my own view of the adaptive function of happiness.

The trouble, Pinker points out, is that happiness doesn’t actually continue for the period of time during which we are enjoying any of these cheerful states. In fact, the longer that any condition persists without change, whether it is illness or health, modest income or prosperity, celibacy or marriage, the more likely we are to drift toward a middling, default attitude that we describe as feeling “content” or “satisfied.”

In reality, we usually describe ourselves as “happy” at those times when we succeed in achieving more than we already have (as the result, for example, of a professional reward) or when we find out that we are a little better off in some way than those around us. Happiness, it seems, is rooted in comparison and newness. For Pinker, this makes it a rather dismal treadmill, an elusive, fleeting, bubbly emotion that was never cut out to serve as the goal for one’s entire life.

Self, Consciousness, and Free Will In the last pages of the book, Pinker writes about some philosophical puzzles that people have never been able to wrap their minds around fully. These are such phenomena as the self (the “I” that we are so aware of), consciousness (our awareness, and our awareness of our awareness) and free will (we insist that our choices and decisions are up to us).

For Pinker the reason these are such enigmas may be that “the mind of Homo sapiens lacks the cognitive equipment to solve them. …Our minds evolved by natural selection to solve problems that were life-and-death matters to our ancestors, not to commune with correctness or to answer any question we are capable of asking” (11570). Such mysteries as the self and free will are holistic phenomena of a kind that does not lend itself to being understood by “the computational apparatus that natural selection has fitted us with” (11639), an apparatus that works methodically from parts to the whole, example to category, cause to effect. Perhaps such a mind just cannot analyze such sensations as the experience of  being alive and being ourselves.

For Pinker then, emotions and sensations are not matters of the heart. Their roots lie in the evolution of the brain, the interaction of brain and culture, and our capacity for a holistic awareness beyond the machinations of the brain itself.