Well, my contention would be that anyone who pays attention to what chimpanzees do in any kind of valid ecological setting will be led into having to explain complex behavior. If you let chimpanzees be chimpanzees, they're going to force you into challenges that have to be explained. One that required explanation with regard to cultural issues was variation: we found different populations of chimpanzees doing different things, and so that had to be explained. As for handedness, if you're looking for the connecting thread, it's this: a lot of the most interesting cultural stuff is object manipulation and tool use. Chimpanzees have an elementary technology. Given that, then the potential is there to look at the way they manipulate these objects, and particularly skillful manipulation. Most of the sorts of criteria we use for handedness are actually based on that kind of manipulation: which hand do you write with, brush your teeth with, whatever. So we asked in the beginning a very simple question: do chimps show this very asymmetrical pattern that humans show of extreme right-handedness?

It initially came with my first collaborator, Caroline Tutin. We started at Jane Goodall's place in Tanzania and thought we had learned what we needed to know about chimpanzees. Then we went to a second site and found, whoops, we didn't know what we needed to know; they were doing things differently. This was the pattern of my career: I'd go to different sites and realize the chimpanzees were doing different things. And other people had the same experience. Pretty soon we had this whole mass of variation that needed to be explained. So that's how the 1999 Nature paper came about (Whiten A., et al., "Cultures in chimpanzees," Nature, 399[6737]:682-5, 17 June 1999).

The article covered the situation five years ago, in terms of which field sites had accumulated enough data that you could actually confidently talk about variation in chimpanzee behavior from site to site. What we realized—"we" being those people who work with wild chimpanzees in various places, whether East Africa, Central Africa, or West Africa—is that we were seeing variation and each of us was describing what we knew, and then reading about what other people were finding. So we thought, "let’s do a collaborative exercise, in which we systematically compare sites across Africa." The nine authors of the Nature piece represent all the big names in chimpanzee field work.

It got a lot of attention, including at least three New York Times pieces. We were pleased and a little bit puzzled when Stephen J. Gould did an op-ed piece in the Times. Delighted, but it was unexpected. He talked about the extent to which a concept like culture could be applied to non-human species. He found it an interesting proposition.

Some of us had been saying it for a while, but we had been voices in the wilderness, in the sense that the world wasn't ready for it. As far back as 1978, Caroline Tutin and I had published a paper on possible social custom in chimpanzees. We published it in an anthropology journal, one of the big journals at the time, and it fell resoundingly flat. No one paid any attention. They thought maybe we were crackpots. Later the data just forced people to take it seriously. People were reporting from different sites saying our chimpanzees don't fish for termites, they crack nuts. And other people were saying, ours don't crack nuts, because there are no nuts, but they fish for driver ants. So the Nature piece has a huge number of categories, and codings that refer to whether the behavior is something that is never seen, occasionally seen, seen all the time, or whether it is ecologically impossible. In other words, you can't hunt a species, like ants, if it's not present. We had to be more sophisticated than just saying whether the behavior was present or absent.

It's been long enough that it's now in the textbooks. That's one form of acceptance. I'm not even sure you could pick up an introductory biological anthropology text these days and not see that paper cited. One reason may be is that the big names are all there. Jane Goodall is there. Everyone known in the field for chasing chimpanzees pitched in.

By itself, that's a fairly notable achievement. We're all a bunch of prima donnas, with our particular chimpanzee populations. To get everybody to kick data into a common pool, and do a single analysis, that's where the credit goes to Andy Whiten. He was the senior author. And he is not a chimpologist. He was the honest broker. He's a very well known primatologist, but in a different area. He's a laboratory guy. We needed somebody detached enough to wrangle us all into line; to get all these big egos to cooperate. And he did an excellent job. He was very diplomatic and very effective.

I won't say that the nine authors were in concert about everything. We had our disagreements and still do. But we decided that in this paper we would let the data speak for itself. There was far less interpretation and more, you might say, ethnography in it. To be fair, Whiten got us together for a second paper two years later, which in the long term will probably be more important than the 1999 paper. It's much more fleshed out. That was published in an ethnology journal called Behaviour. It's not in the in-cites list of highly cited papers, because it's not a social science journal. It's where animal-behavior types publish.

Since the 1999 paper, there have been three similar attempts at synthesis, all loosely modeled on that Nature paper. There's a comparable exercise in orangutans, which was published in Science. And then the capuchin monkey people got together and did a joint paper in 2003. One more attempt was made on a rather limited scale to do a comparison across sites with the bonobos, which is the other species of chimpanzees. Everyone has found similar sorts of variation that cannot simply be explained by environmental or genetic determination, but which seem to require social learning.

I think what we need to do and what we're in the process of doing is moving from the original problem of describing variation to that of explaining variation, in terms of looking at mechanisms. For example, how do habits and patterns of behavior spread? We have a pretty good idea that habits probably spread through female emigration, because in chimpanzees females are the sex that disperse. But we have to look more seriously at what constrains these patterns. Certain things are chimpanzee universals. Others are unique to one population and are never seen anywhere else. In a certain sense, we need to go from ethnography, the description, to ethnology, which is the systematic analysis. Ideally we'll do that in a hypothesis-testing way—that is, it will be theory driven.

In the simplest sense, I started collaborating with another person who was the handedness expert at the time. This was Linda Marchant, and she had really done the first study on chimpanzee handedness, which she published in the early 1970s and which had not been appreciated at that time. We later came to realize it was important. So with my interest in tool use and Linda's in handedness, we started to work on some common ground.

We found that chimpanzees are lateralized, for sure, but that their handedness pattern is not the human pattern. By that I mean, if you ask a human population, which hand do you write with, they will almost always say I write with my right hand all the time. Ten percent will say I always right with my left hand. They don't go back and forth. If you ask a chimpanzee population a comparable question—which hand do you fish for termites with?—50 percent will always use their right hand to fish for termites and 50 percent will always fish with their left hand. They're completely lateralized, but they're evenly split. The distribution is not skewed one way or the other. And it gets even more interesting. That pattern of extreme but balanced lateralization only applies to complex tasks like tool use. It does not apply to ordinary actions like picking up objects, plucking fruit off trees, scratching yourself, etc.

That's a good generalization for chimpanzees in general: they're still surprising us. But yes, it was surprising. Here's another interesting point, for instance, to add to the laterality story. Everything I told you about applies to the study of wild chimpanzees. If you look at chimpanzees in captivity, you get different data. They show what appears to be a weak but consistent right bias for a range of activities. This suggests that maybe captive apes are being inadvertently influenced by their human caretakers. They're around right-handed humans all the time, day in and day out. So maybe they're influenced. That's the hypothesis. It also remains to be tested.

Well, there’s a practical challenge, which is that chimpanzees are threatened and declining in numbers. We have already lost populations of chimpanzees before we even knew them. A population may have gone extinct just recently in the Northeastern Congo, during the battles up there between the Ruwandans and Ugandans and Congolese. They were unique population. They were actually diggers. They would eat underground tubers. We think they got caught up in this whole business and got hammered on multiple fronts. I can’t say for sure that they’re gone. We very much hope they’re not, but the reports have been pessimistic. The general point is that there are populations going all the time, and some have never been properly studied. Once they’re gone, they’re gone forever. We just won’t know. So any scientist who does chimpanzee field studies almost by definition has to be a conservationist. We have to work to protect our subjects.

Well, I think I would go back to an earlier point. I have been chasing chimpanzees for more than 30 years, and I still get surprised in ways that are quite profound. So it’s always serendipitous. Only a couple of years ago, we found a population of chimpanzees in West Africa that uses caves. No one ever suspected this. No one had a clue that chimpanzees used caves. A young post-doc, Jill Pruetz, found this population, and it’s very exciting. And then just this month, in the most recent issue of American Naturalist (in-cites journal interview), a new form of technology was described for some rain forest chimpanzees that we didn't have a clue about. They are using these sticks almost like spades. It’s wonderful stuff. It’s a very exciting field to be in, because the chimpanzees are so interesting. That well is not running dry.