My Great Experience

One of our most basic tools, the No. 2 pencil, used by every test taker, illustrates the exceptional freedom of the human mind as compared with the limited scope of animal cognition. You hold the painted wood, write with the lead, and erase with the pink rubber held in place by a metal ring. Four different materials, each with a particular function, all wrapped up into a single tool. And although that tool was made for writing, it can also pin hair up into a bun, bookmark a page or stab an annoying insect. Animal tools, in contrast such as the sticks chimps use to fish termites out from their mounds are composed of a single material, designed for a single function and never used for other functions. None have the combinatorial properties of the pencil.

Another simple tool, the telescopic, collapsible cup found in many a camper’s gear, provides an example of recursion in action. To make this device, the manufacturer need only program a simple rule add a segment of increasing size to the last segment and repeat it until the desired size is reached. Humans use recursive operations such as this in virtually all aspects of mental life, from language, music and math to the generation of a limitless range of movements with our legs, hands and mouths. The only glimmerings of recursion in animals, however, have come from watching their motor systems in action.

Two eyes positioned above a pair of nostrils that are themselves perched above a mouth such is the layout of the face for vertebrate creatures ranging from sharks to humans. However well that arrangement may be optimized for finding and eating food, among mammals the face has taken on another critical role: communication. Nowhere is this function more apparent than in the human visage. Primates in general have complex social lives, and they commonly use facial expressions in their interactions with one another. We humans have particularly expressive faces with which we convey such emotions as fear, happiness, sadness and anger.

Researchers once chalked up the rich repertoire of human expressions to our having uniquely specialized facial muscles. But physical anthropologist Anne Burrows of Duquesne University has found that, in fact, the chimpanzee the next most dramatic primate differs little from humans in the musculature of its mug. Two features, though, do separate human facial expressions from those of the rest of the primate pack. First, we have distinctive sclerae, or whites, around our irises. Second, our lips protrude from our faces and are darker than the surrounding skin. These traits provide our countenances with strong visual contrasts that may well better telegraph our feelings.