8.3.4.4: Chimpanzees and Bonobos

Chimpanzees and Bonobos: Our Closest Relatives

Of all the primates, chimpanzees and bonobos tell us the most about our own evolutionary history. There are two species: the common chimpanzee (Pan troglodytes) and the bonobo (Pan paniscus). Both share approximately 99% of their DNA with humans, which makes them genetically closer to us than they are to gorillas or orangutans. Yet despite their near-identical genetics, these two species have evolved strikingly different societies, and comparing them gives us a fascinating window into the range of social behaviors that may have existed in our shared evolutionary past.

Two Species, Two Worlds

Like gorillas, both chimpanzees and bonobos are knuckle-walkers, moving on all fours with their weight supported on their knuckles. Chimpanzees are found across tropical Africa and into savanna environments, while bonobos live exclusively in the dense rainforests of the Democratic Republic of Congo, south of the Congo River — a geographic barrier that has kept the two species separated for roughly one million years. Both species split their time between the ground and the trees.

Chimpanzees and bonobos are less sexually dimorphic than the other great apes, though males are somewhat larger than females. Chimpanzees are primarily fruit eaters but are flexible and opportunistic, eating leaves, eggs, insects, and occasionally meat. Chimpanzees and bonobos are also among the only primates, besides humans, that regularly share food, and they do so for remarkably human-like reasons: to support close relatives, to reinforce friendships, and because defending food from persistent group members is sometimes more trouble than it's worth.

The Political World of Chimps

Chimpanzee society is complex, competitive, and there's really no better word for it — political. Troops can number up to 60 individuals, but chimpanzees typically travel and forage in smaller parties that shift in composition throughout the day. Within the larger community, males form a clear dominance hierarchy, maneuvering for status through dramatic displays such as hooting, jumping, dragging objects, and pounding the ground, all designed to intimidate rivals without necessarily resorting to outright violence.

But theatrics and intimidation only go so far. What really determines a male's success is his alliances. Males form tight coalitions cemented through grooming — literally scratching each other's backs. These friendships are long-lasting, strategic, and critically important. A male with powerful allies can challenge individuals he couldn't dominate alone. Chimpanzees remember favors, hold grudges, and will gang up on a dominant individual who has overstepped.

Males remain in the community they were born into for life, which is what makes these coalitions possible. Females, by contrast, leave their natal group when they reach sexual maturity and join a new community — a pattern called female dispersal that reduces inbreeding and shapes the genetic structure of chimpanzee populations.

Male chimpanzees also cooperate to patrol and defend their territory. These patrols are silent and deliberate, and when a patrolling group encounters a lone individual from a neighboring community, the encounter can turn violent. Jane Goodall documented one troop systematically killing all the males of a neighboring group that had splintered off — behavior that struck many observers as disturbingly reminiscent of human intergroup conflict.

The Tool Users

What makes chimpanzee tool use especially interesting is that it varies from population to population. Different communities use different tools in different ways, and young chimps learn by closely watching their mothers. This is not unlike cultural transmission: the passing of learned behaviors across generations, not through genes, but through observation and practice. Of all non-human animals, chimpanzees use tools to solve the greatest range of problems both in the wild and in captivity. And notably, it is female chimpanzees who use tools most frequently. As the primary care providers for their young, they have a compelling reason to be innovative — to increase the chances of survival of their offspring, and her own reproductive success.

Communication and Reproduction

Chimpanzees communicate through a rich repertoire of vocalizations, from soft grunts to the loud, far-carrying pant-hoot, as well as gestures. One of the most recognizable is the outstretched hand, used to request food or reassurance. Interestingly, while humans point to direct others' attention from an early age, chimpanzees do not naturally point in the wild, though they can learn to do so in captivity.

Female chimps have a visible ovulation cycle called estrus, marked by a pronounced pink genital swelling that signals fertility. Males show heightened interest in mating during this period. Male chimpanzees also show a preference for older, more experienced females — a pattern that makes sense given that older females tend to be more competent mothers.

Bonobos: A Different Kind of Ape

Bonobos look remarkably similar to chimpanzees though they are slightly smaller, with darker faces and a more upright posture. It’s their social world that makes them strikingly different. Where chimpanzee society is male-dominated and frequently tense, bonobo society is female-led and largely peaceful. Among bonobos, females form strong alliances with one another through grooming and affiliative behaviors, and it’s these alliances that give females their social leverage. A male bonobo's status is largely determined by his mother's rank—a striking contrast to the coalition-building and competitive displays that define male chimpanzee hierarchies.

Perhaps the most distinctive feature of bonobo society is how conflict is managed. Rather than resolving tension through aggression, bonobos use sexual behavior — including non-reproductive contact between individuals of the same and opposite sex — to ease social stress, reconcile after disagreements, and build social bonds. This happens across genders and is a routine part of bonobo social life. Their use of sex in non-reproductive contexts is more extensive than in any other non-human primate, and in some ways more closely parallels human sexual behavior than that of any other species.

The contrast between chimpanzees and bonobos is one of the most thought-provoking puzzles in primatology. Two species, nearly identical in their DNA, living utterly different social lives. Understanding both species while resisting the urge to see either as a “default” model for our ancestors, gives us a far richer picture of what early human social life might have looked like.