The brain's versatile toolbox

Natural History, Sept, 1997 by Steven Pinker

The human brain is an extraordinary organ. It has allowed us to walk on the moon, to discover the nature of matter and life, and to play chess almost as well as a computer. But this virtuosity raises a puzzle. The brain of Homo sapiens achieved its modern form and size between 50,000 and 100,000 years ago, well before the invention of agriculture, civilizations, and writing in the last 10,000 years. Our foraging ancestors had no occasion to learn astrophysics or to play chess, and natural selection would not have rewarded them with more babies if they had. How, then, did our outsize brain evolve.?

This puzzle led Alfred Russel Wallace, the codiscoverer of natural selection, to defect to creationism, and it has long frustrated our attempts to understand the mind as part of the natural world. But the puzzle can be solved with a key idea: the process of natural selection equipped our ancestors with a mental toolbox of intuitive theories about the world, which they used to master rocks, tools, plants, animals, and one another. We use the same toolbox today to master the intellectual challenges of modern societies, including the most abstruse concepts of modern science.

For more than 99 percent of our evolutionary history, we lived as foragers, and our recent ancestors must have lived much as foraging tribes do today, without any of the trappings of modern civilization. Observing their seemingly simple life, many people have wondered what nonliterate foragers do with their capacity for abstract intelligence. The foragers would have better grounds for asking that question about modern couch potatoes. A foraging life is a camping trip that never ends, but one without Swiss Army knives and freeze-dried pasta.

All foraging peoples use fire and shelters and manufacture many kinds of tools. Their engineering is often ingenious, involving poisons, smokeouts, glue traps, nets, baits, snares, corrals, concealed pits and clifftops, blowguns, and bows and arrows. Animal prey may thus be flushed out, cracked open, trapped, ambushed, or done in by weapons. Plants are cut down or unearthed, shelled and skinned, and detoxified by cooking, soaking, fermenting, and other tricks of the kitchen magician.

How do they accomplish these feats? With the help of language, foragers pool their knowledge and coordinate their actions. Their words offer a window to the kinds of knowledge they possess. All documented human cultures (and by extrapolation, ancestral foraging ones) have words for space, time, motion, number, mental states, tools, flora, fauna, and weather; they make logical distinctions between general and particular, apparent and real, possible and actual. People use these words and concepts to reason about invisible entities such as disease, meteorological forces, and absent animals. They also possess knowledge that is not easily expressed in words. Their mental maps may contain thousands of noteworthy sites, and their mental calendars record cycles of weather, animal migrations, and the life histories of plants.

So we humans evolved mental machinery that allowed us to cooperate and outsmart the local flora and fauna. Vital to that machinery is its ability to analyze and categorize experiences that reflect the world's causal structure, which lets us make good predictions about unseen events. The world is a heterogeneous place, with many kinds of entities -- and laws that make them tick. The mental toolbox we inherited comes equipped with distinct kinds of intuitions -- about space, number, objects, living things, tools, and minds. We can see these intuitions at work as children first try to make sense of their world.

The most fundamental mental tool is an intuitive physics: an understanding of how objects fall, roll, and bounce. Its foundation is an appreciation that the world contains objects that persist when out of sight and that obey laws; it is not a kaleidoscope of shimmering pixels or a magic show in which things disappear and reappear capriciously. In 1890, the philosopher and psychologist William James famously described the world of the infant as a "blooming, buzzing confusion," but recent experiments have shown that babies are not as confused as James thought. Infants as young as three months are apparently interpreting the blooms and buzzes as the outward signs of persisting, law-abiding objects; they are visibly surprised when an experimenter rigs up a display in which objects seem to vanish, pass through each other, fly apart, or move without having been pushed. As one psychologist summed up the results, "a blooming, buzzing confusion" describes the life of the parents, not of the infant.

But some objects do seem to defy physical laws. As the evolutionary biologist Richard Dawkins noted, if you throw a dead bird into the air, it will describe a graceful parabola and fall to the ground, exactly as physics books say it should, but if you throw a live bird in the air it may not touch land this side of the county boundary. These apparent scofflaws are living things, and we interpret them not as weird, springy objects or as law-defying miracles, but as obeying different kinds of laws, the laws of an intuitive biology. Living things are sensed to house an internal essence, which supplies a source of renewable energy, or oomph, that propels animals (usually in pursuit of a goal), gives them their form, and drives their growth and bodily functions.