Introduction to Evolutionary Psychology

We do love a little controversy on the site. Here is a field of study that has as many opponents as it does proponents. Below is our simplified introduction to this complex subject. Two additional pages on the subject contain Leda Cosmides & John Tooby's original early work on the topic.


Why are you reading this?

Why do we do any of the things we do?

Is it possible that nearly 10-million years of developing and adapting to make the best of things in a dog-eat-dog world may have had an effect on us and on the ways we behave?

Our ancestors lived in small, wandering bands that survived by gathering plants and hunting animalsprobably scavenged a bit, toocompeting with (or eluding) animals that were bigger, stronger, and faster. Probably competing with rival bands much like their own. In all kinds of rotten weather . . .

This state of affairs went on and on. Millions of generations. We didn't figure out how to grow food for ourselves until just 10,000 years ago. For that matter, when did you get your first computer? Even if you've had one since birth, you're one of the first generation that could. That's out of 10-million years of human development.

The point is, we worked things outdeveloped as a speciesunder circumstances very different from the world we live in now. So you'd think that an evolutionary perspective could help us to understand human behavior that, since the world has changed so much in recent centuries, may or may no longer be appropriate to our best interests.

But this way of looking at human behavior isn't orthodox. Long before Darwin rocked the status quo in 1859, when he unveiled The Origin of Species, the weight of most scientific thought settled heavily on the idea that the newborn human brain is almost completely blank until sex, lies, videotape, and Mom leave their marks on it. Despite general acceptance (at least by scientists) of the reality of evolution, the belief that nurture trumps nature is de rigueur throughout mainstream anthropology, sociology, and most areas of psychology. It's politically correct, too.

Evolutionary psychology, on the other hand, integrates biology, neuroscience, cognitive science, and anthropology to look at behavior from three angles:

The problems we've endured over 10-million years have been both physical (cold weather, predators, starvation, disease) and social (competition for mates, protection from enemies, cooperation within the group): they exert STRESS on the organism.

The mental mechanisms we've developed to deal with those stresses (kin recognition, cheater detection, mate selection) affect our BRAIN STRUCTURE.

The ENVIRONMENT in which those mechanisms developed may have changed, and thus may change the way the original function is expressed or may render it useless or even destructive.


Assuming that psychology is in fact a branch of biologythe one that studies brains and how they process information and generate behaviorevolutionary psychologists apply five basic biological principles:

1. The brain is a physical system. Its function is to process information and to generate behavior appropriate to the circumstances, and its operation is subject to the laws of chemistry and physics.

2. Neural circuits in the brain were designed by natural selection to solve problems. The environment doesn't stipulate which behaviors are appropriate. The same set of circumstances can elicit different behaviors, depending on the neural circuits that are available to generate them. We've inherited the brain circuits we have because, as our ancestors faced life-or-death problems over the evolutionary millennia, they're the ones that came up with the best solutions.

3. Neural circuits are extremely complex. Most things we do that seem natural, simple, and even reflexive, actually require elaborate webs of neural circuitry, of which we're utterly unconscious. Remember the centipede trying to think which leg to move next. Can you walk and chew gum? How?

4. Neural circuits are specialized for solving different adaptive problems. Using the right tool for the job may be clichd, but you can't beat it for common sense. The Swiss Army knife is a classic problem solver, for instance: one blade doesn't fit all needs. Our bodies are no less masterpieces of functional design: the heart pumps blood, the eyes process light, the liver copes with last night's indulgences . . . and neural circuits of the brain are dedicated to a myriad of specific tasks.

5. The human brain evolved in circumstances very different from our modern world. Because the natural process of selection can take tens of thousands of years to establish even simple changes, our brain developed during the several-million years that we lived in small, nomadic groups of hunter-gatherers. Its circuits were designed to solve the day-to-day problems of those stone-age ancestors.

Because you can, naturally.

The brain directs an organism's behavior according to what's going on around it. It processes information and generates a response. Neuroscientists study the brain's physical structurethe machine itself. Cognitive psychologists study the programs and protocols it useshow it works.

Evolutionary psychologists are interested in functionwhat it does. The physical structure exists because it enables the mental operations that prompt the behavior that solves a problem. That is, solved a problem in the distant past. If circumstances have changed in the last million years, of course, it may make the problem worse. But that's why we have psychologists. That's also why the concept of natural selection is important.

Naturally, the organism with the structure that enables the process that produces the behavior that solves the life-or-death problem will survive to mate, reproduce itself, and live happily (maybe) ever after. The organism that doesn't solve the problem so well, doesn't.

But if form follows function, thenonce that form is selected as the most successful and we're stuck with itdoes it determine function? Even when the ground rules have changed and it screws things up?

The big, bad bugaboo

The controversy roils mostly around the standoff between "nature" and "nurture." It's essentially of the chicken-or-egg variety. Are we born with a brain that's little more than a blank page waiting to be written on by the world around us? Or do we inherit a reference library of instincts and behaviors already machine coded into the apparatus, and resistance is futile?

Probably because evolutionary psychology assumes the existence of specialized neural circuits in the brain, developed to facilitate specific behaviors, and characterized as information-processing devices (sometimes called modules), it may appear to be strictly mechanistic. Cosmides and Tooby, pioneers of the field, write:

The brain is a physical system whose operation is governed solely by the laws of chemistry and physics. What does this mean? It means that all of your thoughts and hopes and dreams and feelings are produced by chemical reactions going on in your head (a sobering thought). The brain's function is to process information. In other words, it is a computer . . . (Evolutionary Psychology: A Primer 1997)


Okay. Sounds pretty mechanical and deterministic. Nature all the way, right? But no; they trash that idea:

Every aspect of an organism's phenotype is the joint product of its genes and its environment. To ask which is more important is like asking, Which is more important in determining the area of a rectangle, the length or the width? Which is more important in causing a car to run, the engine or the gasoline?


Still talking about a physical system, though. This is where evolutionary psychology flirts with political impropriety and gets called unflattering names: racist, sexist, and rigidly conservative (human nature is programmed and thus unchangeable) or, paradoxically, irrationally liberal (human nature is programmed and thus irresponsible).

The core of the controversy seems to be the mind/brain conundrum. Is the mind essentially spirit, resident in the machinery of the brain but somehow independent of it? Or is mind the synergistic product of the staggeringly complex neural circuits of the brain, humming itself a symphony of electrical impulses?

The debate teeters over whether the mind exists to serve the body or the body is simply a mediuma toolfor the mind. But either way, evolutionary psychology looks for the mechanisms of behavior that we all share by virtue of being human, the "evolved structures" that explain why we act the way we do.

For a look in greater detail at Leda Cosmides and John Tooby's original early work on the topic, please see An Evolutionary Psychology Primer and Human by Design.

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