KANZI IS ONE REMARKABLE APE—BONOBO, TO BE precise. He was adopted—kidnapped actually—by the dominant female, named Matata, of a captive colony at the Yerkes Primate Center in Georgia, who, as it happened, was being taught to communicate with humans through lexigraphs, graphic symbols of single words. Matata was not a great student, a bit too old for that sort of thing, but Kanzi proved extraordinarily apt. He had been just sort of hanging around during Matata’s sessions, not paying much attention, seemingly. It soon became obvious, though, that he had observed and learned much, out of the corner of his eye, as it were. When his training became more explicit, he soon learned the meaning of well over 300 symbols, by means of which he could express his desires to his human companions. He also understood spoken English—thousands of words, in fact—which he could translate into lexigraphic symbols by pressing the images on a screen. Even more impressive, Kanzi could communicate verbally, in his normal Chimpansese, with his late stepsister, Panbanisha, over the phone. They had been known to gossip.
There are actually two species of chimpanzees. The one usually displayed in zoos—Pan troglodytes—is by far the most common and the one for which the term “chimpanzee” is usually reserved. Kanzi belongs to the other, far less common species (Pan paniscus), called bonobos, which have a restricted range in the Congo forests. Bonobos were formerly called “pygmy chimpanzees,” though they are no shorter than common chimpanzees. (The name may derive from the fact that they share their forest habitat with small-statured humans formerly known as “pygmies.”) Bonobos are significantly leaner than chimpanzees and have longer legs; their necks are thinner, their shoulders more narrow, and their chests less deep. Bonobos are altogether less robust than chimpanzees, less physically imposing. The bonobo head is also significantly smaller than that of the chimpanzee, with a less protruding snout and smaller brow ridges. On top of the head is a distinctive mop of long hair that tends to form a natural part down the middle.
But it is the behavioral differences between chimpanzees and bonobos that have received the most attention of late. These behavioral differences are much more pronounced than the physical differences and have engendered much discussion for their implications regarding human evolution.
Before bonobos took center stage, chimpanzees were thought to be the best models for extrapolating human behavioral evolution, especially once it was discovered that chimpanzees routinely hunt other primates in an organized and premeditated manner. This finding fit in nicely with a man-the-hunter narrative and certain sociobiological elaborations of its implications, especially regarding putative sex differences in behavior. Also conforming nicely to this narrative is the fact that chimpanzee males are violent, not just individually but often in groups, raiding the territories of adjacent groups. These group conflicts can be quite grizzly and have been touted as the wellspring of human warfare.
Enter the bonobo, the hippy ape. Actually, bonobos embrace the hippy ideal far more than any human hippies ever did, for bonobos are not only pacifist; they also engage in more sex than the most nymphomaniac members of our own species. Rarely do a couple of hours pass without at least some serious foreplay. This rampant sex is also quite promiscuous—partners are ever changing—and indiscriminate with respect to gender. Bonobo lesbian sex is especially rife, and many believe it is the behavior around which bonobo society is organized. For bonobos, in stark contrast to the macho patriarchal chimpanzees, live in a female-dominated society. Male bonobos, like Kanzi, are larger and stronger than female bonobos, but not as much larger and stronger as are male chimpanzees in relation to female chimpanzees. Put another way, bonobos are less sexually dimorphic than chimpanzees. Moreover, whatever size advantage a male bonobo enjoys is outweighed by genitally cemented female bonobo solidarity.
Inspired by the farm fox experiments, Brian Hare and coworkers proposed an overarching explanation for the physical and behavioral differences of chimpanzees and bonobos: that bonobos are, in essence, self-domesticated. They hypothesize that bonobos have experienced natural selection for tameness, from a more chimp-like starting point. Hare equates tameness with lower levels of aggression, but, as we saw with the fox domestication project, a reduction in fear is at least as important an element in tameness as lowered aggression is. Indeed, lowered aggression may be largely a by-product of the nonaggressive.
Richard Francis’s book, Domesticated, is not simply about domestication. It’s a cross disciplinary look at human evolution, biology, culture, psychology and sociology. Over the next few months I’ll be featuring a few tantalizing extended excerpts from this engaging book.
Domesticated: Evolution in a Man-Made World, Richard C. Francis, W. W. Norton, 2015