How High Can Animals Count?

Tests by Hauser and other researchers reveal that monkeys can count up to four. The human ability to count to higher numbers apparently came only after we evolved language and developed words to describe quantities like 25 and 1,000. Some human cultures still don't use large numbers. The Hadza people, hunter-gatherers in Tanzania, for example, have words only for "one," "two," and "three"; anything more is "many." They are aware that a picture with 30 dots displays a larger number than one with 20 dots (as are monkeys), but they have no words for the precise numbers of dots. The bottleneck between human and nonhuman thinking involves not just words, but the ability to recombine words in an endless variety of new meanings. That appears to be a unique human capability. Chimpanzees have a rich social and conceptual life, Hauser maintains, but they can't discuss it with each other. The next step in determining how much thinking ability humans share with other animals will involve scanning the brains of both while they do the same cognitive tasks. Harvard psychologists have already begun to do this in a collaboration with researchers from the University of Massachusetts Medical School in Worcester and the Max Planck Institute in Germany. Monkeys may exhibit the same kind of intellectual behavior as humans, but do they both use the same areas of the brain? "We have a great deal of data that show what areas of the brain are activated when humans respond to various situations," Hauser points out. "Now we will determine if monkeys and other animals utilize the same brain circuits." So far, the monkeys are adapting well to experiments at the University of Massachusetts. They move into harnesses in brain scanning instruments, such as MRI machines, without difficulty. Measurements of their stress levels show that after five days of training, marmoset monkeys feel as comfortable as they do in their home cages with their own social group. For some people, such research will not provide a satisfactory answer to the question: Do animals really think? These people define thinking as having a sense of self, beliefs that go beyond raw perceptions, emotions such as empathy, and the ability to imagine a situation remote in time and place and predict an outcome. "Those capabilities cannot be illuminated by brain scanning," Hauser admits. "But experiments using other techniques are beginning to shed light on what kinds of perceptual and computation skills animals bring to analyzing the world, and in what ways these skills are different from our own."