Not Your Average Ape
by Matthew Huy
With a distribution that now falls entirely within the borders of the war-torn Democratic Republic of Congo, the bonobo (Pan paniscus) is one of the many victims of the bushmeat trade. While conservationists struggle for solutions, behaviorists are slowly unraveling the mysteries of these primates’ otherwise peaceable societies.
Scientists didn’t initially recognize the distinction between bonobos and chimpanzees (Pan troglodytes). But in 1929, the German anatomist Ernst Schwarz inspected the skull of what was thought to be a juvenile chimpanzee in Belgium’s Tevruren Museum, and noticed something peculiar. The sutures along the cranium were fused, implying maturity. Schwarz concluded that this specimen, labeled as an adolescent based on its size, was in fact a mature adult—and thus a new species, christened Pan paniscus. DNA analyses now suggest that chimps and bonobos in fact diverged about 2.5 million years ago.
Based on its seemingly small size, the bonobo was given the common name "pygmy chimpanzee" This moniker was ultimately rejected, for bonobos differ in size from chimpanzees only slightly. Male bonobos weigh on average about 95 pounds, females about 80 pounds; individuals of the lightest of the three subspecies of chimpanzee weigh roughly the same. Bonobos and chimpanzees do diverge geographically, however. All wild chimps live north of the Congo River across the belt of Africa; bonobos today inhabit la cuvette centrale, Africa’s lush central basin, south of the Congo River in the Democratic Republic of Congo. Anywhere from 5,000 to 100,000 bonobos are estimated to remain in the wild, and the remoteness—and frequent civil unrest—of their home range has made thorough field studies nearly impossible.
Nevertheless, three decades of sporadic study have gradually exposed the secret lives of these sociable apes. Bonobos, scientists report, typically form communities of 40 to 120 individuals. During the day, bonobos break into smaller parties of mixed sexes and ages to forage for fibrous foods like fruits, herbs, and plant stems, or invertebrates like earthworms and millipedes. Nearly every night, the entire community comes together again to sleep in nests high up in the trees.
Unlike chimpanzees—which many anthropologists long regarded as models for human ancestral behavior—bonobos live in societies governed more by cooperation than by conflict. Bonobos’ array of social behavior, including animated displays, grooming, and sexual relations, may serve to reduce tension and violence within large groups. Although squabbles between male bonobos are common, serious physical violence or injury is rare. Instead, sexual behavior serves as the primary social currency in bonobo life. Bonobos use sex to reconcile with other group members, to exchange for food, and to relieve aggression, as primatologist Frans de Waal describes in vivid detail in his book, Bonobo: The Forgotten Ape. "The chimpanzee resolves sexual issues with power; the bonobo resolves power issues with sex," writes de Waal.
In contrast to chimpanzees, in which males dominate females, female bonobos usually best males in clashes over food. Adolescent female bonobos migrate out of their natal communities to join a new group; juvenile males remain behind with their mother group. Nonetheless, alliances between unrelated females in a group are solidified through grooming and sexual behavior. Such bonding allows female bonobos—who are slightly smaller and lack the large canine teeth of their male peers—to join together to defeat a single male.
Male bonobos act according to a rigid system in which higher-ranking males mate more often than lower-ranking ones. It might actually be the females who control the male hierarchy. In addition to being protective, bonobo mothers help determine their son’s rank. Stronger, more aggressive females clash with other mothers and may pave the way for their sons’ rise up the social ladder. In the drama of bonobo dominance, males appear to play the puppets, and females the puppet-masters.
Of all living primates, it is the occasionally upright bonobo—not the chimpanzee or gorilla—that most closely resembles early hominid ancestors in anatomy, and perhaps in behavior. Modern humans indeed look more like bonobos than any other species. We share 98 percent of the same DNA. We may even share many of the same emotions—including, happily, the gift of empathy.
De Waal tells a story of a juvenile bonobo at the Twycross Zoo in England discovering an injured starling in her enclosure one day. The young ape took the bird in her hand, climbed to the top of a nearby tree, and began raising and lowering the creature’s wings before throwing the bird in the air. She was trying to teach it to fly.
Bonobos and other primate populations across Africa are vanishing on account of poaching as well as habitat loss. Whether people extend our closest cousins a helping hand remains to be seen.
—Matthew Huy
ZooGoer 30(5) 2001. Copyright 2001 Friends of the National Zoo. All rights reserved.
