Our Inner Ape

Primatologist Frans de Waal argues that human nature can be understood only by examining both of our closest living relatives: the chimpanzee, known for its hierarchical aggression, and the bonobo, a lesser-known ape celebrated for its peacefulness and hypersexuality. Rather than the purely selfish, violent creature depicted by decades of popular biology, the human species is a "bipolar ape" whose moral and immoral tendencies alike have deep evolutionary roots.

De Waal opens by challenging the assumption that nature accounts only for our worst qualities. He contends that empathy and fellow-feeling are as much a part of our biological heritage as power and sex. At the Twycross Zoo in Great Britain, a bonobo named Kuni found a stunned starling, climbed a tall tree, carefully unfolded the bird's wings, and launched it toward freedom, tailoring her help to an animal entirely unlike herself. At Chicago's Brookfield Zoo in 1996, a gorilla named Binti Jua scooped up a three-year-old boy who had fallen into the primate exhibit and carried him to safety. These acts of cross-species sympathy reveal capacities long dismissed by scientists fixated on animal ferocity. De Waal introduces the book's guiding metaphor: Humans stand like a Janus head, the two-faced Roman god, with one face compassionate and the other cruel, each corresponding to one of our two closest relatives.

Bonobos, not identified as a separate species until 1929, are egalitarian, female-dominated, and resolve tensions through sexual contact rather than aggression. Chimpanzees are hierarchical, politically cunning, and capable of lethal violence. The two species belong to the same genus, Pan, and are equally close to humans genetically, having diverged from each other roughly 2.5 million years ago after both split from the human lineage about 5.5 million years ago. De Waal notes that the bonobo's obscurity stems partly from the fact that its peacefulness and eroticism did not fit prevailing ideas about human nature as inherently violent.

De Waal traces the intellectual tradition he aims to overturn. After World War II, the Austrian ethologist Konrad Lorenz and the American journalist Robert Ardrey popularized the "killer ape" myth, casting aggression as hardwired. Later, evolutionary biologist Richard Dawkins's The Selfish Gene extended this bleak view by depicting selfishness as evolution's driving force. De Waal calls this framework the "veneer theory": the claim that human decency is a thin cultural overlay hiding a brutal core. He counters with what he terms the "Beethoven error," the assumption that an ugly process must produce ugly products. Natural selection has generated both predatory fish and pilot whales so attached to one another that they beach themselves together. Darwin himself believed morality was grounded in social instincts shared with other animals, and brain scans confirm that moral decision-making activates ancient emotional centers, not merely the neocortex, the brain's outer layer associated with higher reasoning.

The book's treatment of power centers on the fate of Luit, a male chimpanzee at the Arnhem Zoo in the Netherlands who was killed by two rivals, Nikkie and Yeroen. Yeroen, an aging former alpha, had helped the younger Nikkie overthrow Luit years earlier, and the two ruled as a team until Nikkie curtailed Yeroen's sexual privileges. This rift allowed Luit to reclaim dominance. Unable to tolerate a second loss of power, Yeroen coordinated with Nikkie in a brutal nighttime attack. De Waal argues that this episode illustrates a universal principle: No chimpanzee male can rule alone. Coalition-building, community acceptance, and political finesse are as essential among chimpanzees as in human politics. He draws parallels to political assassinations and to the psychological devastation leaders experience upon losing power, comparing Yeroen's weeks of despondency after an earlier dethronement to Richard Nixon's breakdown upon resigning the presidency.

Female power takes a different form. At the San Diego Zoo, de Waal observed female bonobos using genito-genital rubbing, or GG-rubbing, to cement alliances and collectively dominate males. In wild bonobo society, male rank depends on a mother's status. De Waal describes a wild alpha female named Kame whose three grown sons held high positions until Kame weakened with age and died after being defeated by a rival mother, at which point her sons dropped in rank. He applies coalition theory to broader politics, introducing the "strength is weakness" paradox: The most powerful player is often the least attractive ally because joining forces with that player adds little leverage. He argues that egalitarianism in small-scale human societies is not a passive state but an actively maintained condition enforced through ridicule, gossip, and sometimes lethal force against would-be tyrants. Democracy, he concludes, satisfies two tendencies at once: the will to power and the desire to hold it in check.

The book's treatment of sexuality centers on the bonobo's repertoire, including face-to-face copulation, GG-rubbing, mutual penis rubbing, and other combinations, with an estimated three-quarters of sexual activity serving social rather than reproductive purposes. De Waal describes bonobos as "pansexual" and argues that their behavior undermines the notion that homosexuality is an evolutionary puzzle. He traces bonobo hypersexuality to the prevention of infanticide. American anthropologist Sarah Blaffer Hrdy formalized the hypothesis that males kill infants they could not have sired to hasten females' return to fertility. Bonobo females counter this threat by mating with many males and maintaining genital swellings even when not fertile, confusing paternity so that no male can safely attack any infant. Human sexuality, de Waal argues, took a different path: The nuclear family arose on the savanna, where vulnerable females needed committed male protectors. By increasing a male's confidence in his paternity, the pair-bond gave him incentive to invest in child care and in collective enterprises such as hunting and governance.

Turning to violence, de Waal distinguishes human warfare from animal aggression, noting that armies require command structures and indoctrination that apes lack. He describes wild chimpanzees conducting silent border patrols and killing lone males from neighboring communities in coordinated attacks, drawing on his visit to the field camp of chimpanzee researcher Toshisada Nishida in Tanzania's Mahale Mountains. He connects these behaviors to human psychology through the Stanford Prison Experiment, in which college students assigned guard roles became abusive within days. Yet bonobos offer a contrasting model: At Wamba Forest in the Democratic Republic of the Congo, different communities mingled peacefully for an entire week, and no fatalities between bonobo groups have ever been recorded. De Waal attributes this peacefulness to female dominance, which renders male territorial competition pointless. He also examines conflict resolution, describing an experiment in which quarrelsome juvenile rhesus monkeys housed with more tolerant stumptail monkeys developed lasting peacemaking skills, demonstrating that the capacity for reconciliation is learned rather than instinctive.

De Waal argues that empathy is grounded in biology rather than culture, tracing it from contagious emotional responses to sophisticated perspective-taking. He describes "mirror neurons," brain cells activated both when performing an action and when watching another perform it, and notes that apes perform targeted helping, assistance tailored to another's specific predicament. This capacity emerges alongside mirror self-recognition in human children around 18 months of age. Psychologist Joshua Greene's trolley dilemma experiments, in which participants readily divert a runaway trolley to kill one person instead of five but balk at physically pushing someone to achieve the same outcome, show that moral decisions activate emotional brain centers rather than purely rational ones. De Waal examines reciprocity as another building block of morality: Chimpanzees who groom a particular individual in the morning are more likely to receive food from that individual later, and capuchin monkeys refuse to work when they see a partner receiving better rewards for the same task, a reaction he identifies as the evolutionary precursor to the human sense of justice.

In his concluding chapter, de Waal rejects both the Hobbesian view of humans as reluctant social contractors and the purely optimistic view of innate goodness. He warns that apes face extinction and that losing them would diminish our understanding of ourselves. He critiques both Communist collectivism, which failed by suppressing individual ambition, and unmitigated capitalism, which he argues is unsustainable because it denies basic solidarity. The political system best suited to human nature would balance self-interest with community spirit, mimicking the small-scale societies in which our ancestors evolved. Our morality, far from being an illusion, is a genuine product of evolution, and empathy is the one capacity that can overcome our innate xenophobia.