The vervet fear of snakes is shared by baboons, chimps, and many other primates. You expose wild rhesus monkeys to snakes and objects that look like snakes and they jump out of their skins. Do the same experiment with laboratory-raised rhesus monkeys who have never seen a snake and, although some of them are afraid, you find that they’re much less distraught. In one experiment the wild chimps’ snake phobia became almost manageable when every time the chimp saw a snake it also was offered a banana.11 So is the fear of snakes not hereditary, but somehow taught by mothers to their babies? Or is there an inborn fear that’s softened in laboratory monkeys because they become habituated to harmless, snake-like objects—hoses, for example? Which is it: heredity or environment? Is knowledge of what a snake looks like, and that snakes mean primates no good, encoded in the DNA? Or are baby primates just watching adults closely and copying what they do?
Almost certainly the answer is a mix between the two. There seems to be an inborn snake-aversion program in the brains of primates. But this is not a closed program, inaccessible to new information from the outside world. Instead it’s an open program that can be modified by experience—for example, “I’ve seen a lot of snakes in my time that don’t do me much harm, so I’ll be a little more relaxed around them,” or, “Every time I see a snake, a banana miraculously appears; snakes have their good points too.” Most primate programs are open, adaptive, malleable, adjustable to new circumstances—and therefore necessarily partaking of ambivalence, complexity, inconsistency.
In a typical modern chronology,12 the line that would lead to us split off from Old World Monkeys about 25 million years (m.y.) ago; from the gibbons, 18 m.y. ago; from orangutans around 14 m.y. ago; from gorillas some 8 m.y. ago; and from the chimps approximately 6 m.y. ago. Bonobos and common chimps went their separate ways only about 3 m.y. ago. Our genus, Homo, is 2 million years old. Our species, Homo sapiens, is maybe 100,000 to 200,000 years old—the equivalent of the last day in the life of that fifty-year-old.
Committed to a communal social life, under intense selection pressure from predators, with brains evolving rapidly and education of the young effectively institutionalized, the primates have been developing new forms of intelligence. Their curiosity, experimental bent, and intellectual quickness are partly responsible for their success.
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Here is an account, by a Japanese primatologist, of a remarkable set of events that transpired in a colony of macaques isolated on a small island called Koshima. Initially, in 1952, there were only twenty of the monkeys; the number almost trebled over the following decade. The natural food supply on Koshima was inadequate, so the monkeys had to be provisioned—with sweet potatoes and wheat dumped on the shore by the primatologists who were observing them.
As anyone knows who’s ever been to a picnic at the beach, sand sticks to food and makes it unpleasantly gritty. In September 1953 a one-and-a-half-year-old female named Imo figured out that she could rinse the sand off her sweet potatoes by dunking them in a nearby brook.After Imo, the next individual to learn potato washing was Imo’s playmate, who did so in October. Imo’s mother and another male peer began to wash in January 1954. In subsequent years (1955 and 1956), three of Imo’s lineage (younger brother, elder sister, and niece) and four animals from other lineages (two were a year younger and two were a year older than Imo) started to do so. Thus, with the exception of her mother, all the individuals that learned potato washing quickly were either peers or young close relatives of Imo …After 1959, features of information transfer changed. Sweet potato washing was no longer a new mode of behavior: when infants were born, they found most of their mothers and elders washing potatoes and learned this behavior from them as they learned the group’s usual food repertoire. Infants are taken to the edge of the water during the period when they are dependent on mothers’ milk. While their mothers wash potatoes, infants watch carefully and put into their mouths pieces of potatoes that mothers drop in the water. Most of the infants acquire potato washing around 1 to 2.5 years old …[I]n the second period (1959-present, the period of “precultural propagation”), acquisition of potato washing occurred independent of sex and age. During the second period, virtually all individuals … acquired this habit through their mothers or playmates when they were infants or juveniles.
But there was still the problem of sandy wheat—until Imo’s second epiphany:In 1956, when Imo was 4 years old, she took a handful of mixed wheat and sand to the brook. When it was dropped on the water, the sand sank and the floating wheat could be skimmed off the water’s surface, now clean again. This “placer-mining” technique* was also adopted by some of the other monkeys, and soon more and more animals learned it …Compared to potato washing, placer mining was quite slow to propagate …Placer mining appears to require more understanding of complex relations between objects and may be particularly difficult to learn because a monkey must “discard” his food first, while in potato washing he can keep the potato from the beginning to the end.13
Imo was a primate genius, an Archimedes or an Edison among the macaques. Her inventions spread slowly; macaque society, like traditional human societies, is very conservative. Perhaps the fact that she came from a high-ranking family in a species given to hereditary matriarchy aided acceptance. As is usually true, adult males were the slowest to catch on, obstinate to the last; a female invented the process, other females copied her, and then it was taken up by youngsters of both sexes. Eventually, infants learned it at their mother’s knee. The reluctance of the adult males must tell us something. They are fiercely competitive and hierarchy-ridden. They are not much given to friendships or even to alliances. Perhaps they felt impending humiliation—if they were to imitate Imo, they would be following her lead, becoming in some sense subservient to her, and thereby losing dominance status. They would rather eat sand.
No other group of macaques anywhere in the world is known to have made such inventions. By 1962, it is true, macaques on other islands and the mainland, recently provisioned with potatoes, began washing their food before eating it. But it is unclear whether this was due to independent invention or to cultural diffusion: In 1960, for example, Jugo—a macaque who had become adept at washing potatoes—swam from Koshima to a nearby island where he stayed for four years and may have trained the resident macaques.14 Perhaps there were other macaque Archimedes; perhaps not. Imo is the only one we know for certain.
It took a generation for these two obviously useful inventions to become widely accepted.15 The conservative, near immobility of popular prejudice, the reluctance to adopt a new practice even if its advantages are clear, is a tendency not restricted to Japanese macaques.16 Perhaps the stolidity of the adult males is partly a matter of learning abilities declining with age. Human teenagers seem so much more adept than their parents at, say, operating a personal computer or programming a videocassette recorder. But this doesn’t explain why adult female macaques learned so much more readily than their male counterparts.