When looking at baboon research, a common question arises: Why baboons and not some other species which is smarter and more closely related to humans? Its a question I know that I asked when I began to look into participating in primatology research. The best known of our closest primate relatives is the chimpanzee, an animal which is endangered, but still studied heavily. Why baboons and not chimps?
Well, there are the lame answers - baboons are more common and thus easier to study. They live in more easily accessibly locations, and plenty of them aren't endangered so you don't have to go around worrying so much about protecting their rights when you pick up their poop in the forest, and fly it to the northern hemisphere where you can analyze it.
However, what I (and a slew of others, of course) see as the key difference between baboons and chimpanzees is in the magnitude of their sociability. Chimps are very social animals, of course, but their maximum group size is about 60 to 70 individuals. Baboons, on the other hand, have groups which can be 100 individuals strong. A classic South African baboon book written in the 20's by a naturalist describes a troop of more than three hundred individuals.
This is a pretty big difference. Baboons have smaller brains than chimps, but they know who every individual in a troop is, they know their social rank and relations to others in the hierarchy, and they know who is descended from who, and all kinds of more complex blood relations. Chimps know much of this as well, but baboons are aware of it on effectively double the scale.
So why do we care?
Baboons provide powerful evidence in support of what ethologists call the "social intelligence hypothesis," which basically argues that the enlargement of the human brain was driven by increased complexity in social living and group size. One of the major competing hypotheses argues that increasing technological proclivity drove the development of our brains. Chimps support this hypothesis, as they excel at tool use.
How do the behaviors of two primates, baboons and chimpanzees, compare to those of humans? Humans are highly adept both socially and technologically; scientists of course admit that both factor played key roles, but which influence played the more crucial role in human development? Human maximum group size is on par with that of baboons, and far exceeds that of chimps... For very particular reason which I will get into another time (soon!), human groups should be 3 times as large as chimp groups, yet we manage to form significantly larger stable groups.
Why can we and the baboons manage to exceed expected group size? On the whole, baboons are less intelligent than chimps but still maintain bigger groups - so maybe the mental methods of baboon social intelligence are similar to our own which we use to establish such massive groups. Maybe social intelligence isn't even the most important of the hypotheses, but as long as there are correlates between us and the baboons, we stand to learn something from them about how our brains and behavior are designed to handle the complex social situations we encounter daily.
And that, is why we study baboons.
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I'm afraid the social intelligence hypothesis is highly dubious at best. It makes several predictions, none of which is, as far as I can recall, borne out by observable facts. The fact that pongids have much larger brain sizes than monkeys while probably having smaller social groups than our direct monkey ancestors is a point against it. The increase in cranial capacity in apes was probably not being driven by the need to maintain social networks.
ReplyDeleteAn even more important indication that our brain size did not evolve primarily to manage social networking is that we are capable of supporting much larger interpersonal networks than our ancestors 100,000 to 200,000 ya probably lived in (based on archeological evidence). If dealing with these social groups was the driver, we would be unable to cope with the much larger numbers of acquaintances that individuals have begun to have in the last 6000 to 10000 years (since the development of civilization and before that agriculture). We have not evolved appreciably in that time. If social intelligence was the main driver for increased capacity, increases in brain size to account for social groups larger than those actually present in distant prehistory would not have been adaptive; brain size would be matched to whatever tribe size was actually prevalent. Yet that we have been able to manage the huge increase in social group size shows that we possess mental processing power far in excess of what the first homo sapiens could have needed for social purposes. In other words, our brain size was far beyond what social considerations required, which is strong evidence that something else was more important in driving the evolution of intelligence.