When I am in the field, I study particular aspects of great ape behavior that I have spent years reading about and preparing to observe. I follow chimpanzees, as well as some of the prey animals the chimpanzees like to hunt, and record the apes' behavior using notebooks, video, and still photography. Only by spending long periods in the field can one hope to see the amazing things chimpanzees and other primates do with their lives.

You might think that studying a particular group of animals for more than 30 years would be long enough to tell us all we need to know about it. But consider this. If extraterrestrial scientists came to Earth to study people, how long would they have to observe you and your family before they could say they had learned everything of importance about the whole human species? The answer is, of course, a very long time, and even then they would need to observe a variety of societies in a variety of places.

Each decade since the 1960's has brought new and exciting discoveries about the great apes. In the 1970's, after 15 years of closely observing wild chimpanzees, Goodall and her students first reported one of the most astonishing of all her discoveries about chimpanzee behavior—murder and warfare. Indeed, among primates, only chimpanzees and human beings engage in such brutal acts.

Field studies in the late 1970's—starting with those of Caroline Tutin of the Centre International de Recherches Médicales, a primate research center in Franceville, Gabon—revealed that gorilla social groups often have more than one male. This was a surprising development, as primatologists had previously thought that gorillas lived only in “harems” made up of one male and several females. Primatologists such as Tutin also witnessed gorillas in parts of Africa eating fruit rather than leaves, traveling long distances, and otherwise behaving quite differently from the gorillas Fossey had studied.

In the 1980's, scientists realized that chimpanzees in some parts of Africa use stone tools to crack open nuts. In the 1990's, researchers learned how frequent and intense chimpanzee hunting and meat-eating can be. And only in the early 2000's have we begun to appreciate the differences in culture in great ape societies. Culture is the learned beliefs and practices of a society.

One of the most fascinating examples of cultural diversity (differences) among chimpanzees involves their choice and use of tools. For example, in a forest in East Africa, a chimpanzee sits by a gigantic termite mound. He pokes a hole in the mound with his finger, then inserts a thin stick. Hundreds of huge-jawed soldier termites swarm over the stick to protect their nest. The chimpanzee gently withdraws his tool and swipes it through his mouth, licking off and chewing the insects. He endures the many termite bites he receives for the sake of a tasty snack rich in protein and fat.

Meanwhile, in a forest 3,200 kilometers (2,000 miles) away in western Africa, another chimpanzee sits under a nut tree pounding walnut-sized nuts open with a stone hammer. The meat inside is fatty and delicious. He has learned to do this by watching his mother and is now an expert nutcracker himself.

The termite-fishing chimpanzee in eastern Africa does not use stone tools, even though there are plenty of rocks and nuts in his forest. The stone-hammering chimp in western Africa does not fish for termites, even though there are many of the insects' huge mounds in his habitat. These behaviors are not, as far as we know, determined by the chimps' environment. If they were, then we would expect to see similar tools in similar forests, which we do not. These preferences for certain tools represent differences in chimpanzee culture, similar to the differences in styles of human homes, for example. Scientists have found some evidence for cultural diversity in the other three groups of great apes, though it appears to be much less common than among chimpanzees.