Are We Smart Enough to Know How Smart Animals Are?(25)

When it comes to tool use, chimps always catch the limelight, but there are three other great apes—bonobos, gorillas, and orangutans—that, together with chimps, us, and the gibbons, make up the Hominoid family. Not to be confused with monkeys, Hominoids are large, flat-chested primates without tails. Within this family, we are closest to chimps and bonobos, both of which are genetically nearly identical to us. Naturally, there is heated debate about what the minuscule-sounding 1.2 percent DNA difference between us and them exactly means, but that we are close family is not in doubt. In captivity, the orangutan is an absolute master tool user, dexterous enough to tie knots into loose shoelaces, and to construct instruments. One young male was seen to join three sticks, which he had first sharpened, into two tubes to build a five-section pole to knock down suspended food.25 Being notorious escape artists, orangs may dismantle their cage so patiently, from day to day and week to week, while keeping dislodged screws and bolts out of sight, that keepers fail to notice what they are doing until it’s too late. In contrast, until recently all we knew about wild orangs was that they sometimes scratched their butt with a stick or held a leafy branch over their head during rain. How could a species that is so talented offer so little evidence of tool use in the wild? The inconsistency was resolved when, in 1999, the tool technology of orangutans in a Sumatran peat swamp came to light. These orangs extract honey from bee nests with twigs and use short sticks to remove the seeds embedded in the stinging hairs of neesia fruits.26

The other ape species, too, are perfectly capable of tool use, and we have already laid to rest the view that gibbons lack this capacity.27 But reports from the wild remain meager to nonexistent, sometimes suggesting that only chimps are proficient tool users. We see glimpses, such as when gorillas preventively disarm poacher snares, which requires a grasp of basic mechanics, or traverse deep water. When elephants had dug a new water hole in a swampy forest in the Republic of Congo, the German primatologist Thomas Breuer saw a female gorilla, Leah, try to wade across. She stopped when she was waist-deep into it, however—apes hate swimming. Leah returned to shore to pick up a long branch to gauge the water’s depth. Feeling around with her stick, she walked bipedally far into the pool before retracing her steps to return to her wailing infant. This example highlights the shortcomings of Beck’s classical definition, because even though Leah’s stick altered neither anything in the environment nor her own position, it did serve as a tool.28

Chimpanzees are recognized as the most versatile primate tool user apart from us, but this heralded position has been challenged. The challenge did not come from any Hominoid but from a small South American monkey. Brown capuchin monkeys have been known for centuries as organ-grinders and more recently as trained helping hands for quadriplegics. They are extremely manipulative and particularly good at tasks that tap into their tendency to smash and bang things. Having had a colony of these monkeys for decades, I know that almost anything you hand them (a piece of carrot, an onion) is going to be pounded to mush on the floor or against the wall. In the wild, they pound oysters for a long time until the mollusk relaxes its muscle so they can pry it open. During the fall, our monkeys in Atlanta collected so many fallen hickory nuts from nearby trees that we’d hear frantic banging sounds the whole day in our office adjacent to the monkey area. It was a happy sound, because capuchins seem to be in their best mood when they are doing things. Not only did they try to break open the nuts, they also employed hard objects (a plastic toy, a block of wood) to smash them with. About half the members of one group learned to do so, whereas the second group never invented the technique despite having the same nuts and tools. This group obviously consumed fewer nuts.

Capuchins’ natural predisposition to be persistent pounders sets them up for nut cracking in the field. A Spanish naturalist first reported it five centuries ago, and more recently an international team of scientists found dozens of cracking sites in the Tietê Ecological Park and other sites in Brazil.29 At one site, capuchins eat the pulp of a large fruit, after which they drop its seeds to the ground. They return a couple of days later to collect those seeds, which by then have dried out and are often infested with larvae, which the monkeys are fond of. Traveling with the seeds stuffed in their hands, mouth, and (prehensile) tail in search of a hard surface, such as a large rock, the monkeys would get a smaller stone to pound the seeds with. While these stones are about the same size as those used by chimps, the capuchins are only about the size of a small cat, so their hammers weigh about one-third of their body! Literally acting as heavy equipment operators, they lift them high above their heads to get a good hit. When the tough seeds are cracked, the larvae are there for the picking.30

Capuchin nut cracking thoroughly upset the evolutionary narrative that had been woven around humans and apes. According to this story, we are not the only ones who knew a Stone Age: our closest relatives still live in one. To stress this point, a “percussive stone technology” site (including stone assemblies and the remains of smashed nuts) was excavated in a tropical forest in Ivory Coast, where chimpanzees must have been opening nuts for at least four thousand years.31 These discoveries led to a human-ape lithic culture story that fit together nicely, tying us to our close relatives.

This is why the discovery of similar behavior in a more distant relative, such as the capuchin monkey—equipped with tails by which they can hang!—was met with surprise and initial grumbling. The monkeys didn’t fit. The more we learned, however, the more the nut cracking by capuchins in Brazil began to resemble that of chimpanzees in West Africa. Yet capuchins belong to the neotropical monkeys, a distant group that split off 30 to 40 million years ago from the rest of the primate order. Perhaps the similar tool use was a case of convergent evolution, since both chimps and capuchins are extractive foragers. They break things open, destroy outer shells, and smash things to pulp in order to eat, which might be the context in which their high intelligence evolved. On the other hand, since both are large-brained primates with binocular vision and manipulative hands, there is an undeniably evolutionary connection. The distinction between homology and analogy is not always as clear as we’d like it to be.