Field of Science

How are monkeys and humans different (I mean, besides the tail)

Marc Hauser, one of a handful of professors to be tenured by Harvard University (most senior faculty come from other universities), has spent much of his career showing that non-human primates are smart. It is very dangerous to say "Only humans can do X," because Hauser will come along and prove that the cotton-top tamarin can do X as well. Newborn babies can tell Dutch from Japanese? Well, so can the tamarins.

For this reason, I have wondered what Hauser thinks really separates human cognition from that of other animals. He is well-known for a hypothesis that recursion is the crucial adaptation for language, but I'm never sure how wedded he is to that hypothesis, and certainly he can't think the ability to think recursively is all that separates human thought from tamarin thought.

Luckily for me, he gave a speech on just that topic at one of the weekly departmental lunches. Hopefully, he'll write a theory paper on this subject in the near future, if he hasn't already. In the meantime, I'll try to sketch the main point as best I understood it.

Hauser is interested in a paradox. In many ways, non-human primates look quite smart -- even the lowly tamarin. Cotton-top tamarins have been able to recognize fairly complex grammatical structures, yet they do not seem to use those abilities in the same ways we do -- for instance, they certainly don't use grammar.

In some situations, non-human primates seem to have a theory of mind (an understanding of the contents of another's mind). For instance, if a low-ranking primate (I forget the species, but I think this was with Chimpanzeees) sees two pieces of good food hidden and also sees that a high-ranking member of the troop can see where one piece was hidden but not the other, the low-ranking primate will high-tail it to the piece of food only he can see. That might seem reasonable. But contrast it with this situation: these primates also know how to beg for food from the researchers. What if primate is confronted with two researchers, one who has a cloth over her eyes and one who has a cloth over her ears. Does the primate know to beg only from the one who can see? No.

Similarly, certain birds can use deception to lure a predator away from their nest, but they never use that deceptive behavior in other contexts where it might seem very useful.

These are just three examples where various primates seem to be able to perform certain tasks, but only in certain contexts or modalities. Hauser proposes that part of what makes humans so smart are the interfaces between different parts of our brains. We can not only recognize statistical and rule-based regularities in our environment -- just like tamarins -- but we can also use that information to produce behavior with these same statistical and rule-based regularities. That is, we can learn and produce grammatical language. We can take something we learn in one context and use it in another. To use an analogy he didn't, our brains are an office full of computers after they have been efficiently networked. Monkey computer networks barely even have modems.

This same theory may also explain great deal of strange human infant behavior. More about that in the future.

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