Chimpanzee

• 1. Introduction

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  Pan troglodytes shares 99% of its DNA with the human species, yet for most of human history, the creature we now call the chimpanzee was little more than a rumour in Europe. The name itself first appeared in print in The London Magazine in 1738, glossed as meaning "mockman" in a language of "the Angolans". That word, so close to mockery and yet so full of recognition, captures everything that has made this animal so difficult for humans to reckon with. Are chimpanzees a mirror, a curiosity, or a warning about what we are? This is the story of a species that has been a source of scientific astonishment, ethical argument, and ecological crisis all at once. How did chimpanzees evolve alongside humans? What does their behaviour reveal about the origins of intelligence, war, and language? And why, after surviving millions of years, is their future now in serious doubt?

• 2. Deep Roots, Close Kin

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  Bonobos and chimpanzees split from the human lineage about 8 million years ago, according to studies published in 2017 by researchers at George Washington University. Then, roughly 2 million years ago, bonobos separated from the common chimpanzee line. That sequence matters because it means chimpanzees are not a relic or a stepping stone. They are a fully evolved species on their own branch of the primate family tree, one that diverged from humans across millions of years of independent history.

  Anthropologist Alice Roberts notes that at least 24 species of hominin appeared after that initial divergence, only one of which survives today. The chimpanzee genome, first drafted in 2005, confirmed that roughly 99% of genetic code sequences are shared between our two species. A more complete genome published in 2025 complicated that figure: when entire DNA strands are examined, including insertions, deletions, and non-coding material, the differences increase to almost 15%. Those differences cluster in genes related to the brain, immune system, and aging.

  Chimpanzees have 24 pairs of chromosomes to the human 23. That discrepancy traces to a fusion of two chromosomes during human evolution, producing human chromosome 2. A 2006 study concluded that around 6% of genes in chimpanzees and humans differ in copy number, and a 2012 study of brain tissue found that the two species diverged significantly in how genes are switched on and off. The genetic closeness is real, but so is the complexity.

• 3. Body and Territory

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  Adult male chimpanzees weigh around 40 kg in the wild. Females average around 30 kg. In captivity, certain individuals have stood over 168 cm on two legs and weighed up to 136 kg. The body is built for climbing: arms longer than legs, an opposable big toe that grips branches, and muscles that are 50% stronger per unit of weight than human muscles due to a higher content of fast-twitch fibres. Japan's Asahiyama Zoo has estimated the grip strength of an adult chimpanzee at 200 kg, with other sources citing figures as high as 330 kg.

  The chimpanzee brain is around 66% smaller than the human brain, with an average endocranial volume of 400 cm3 against 1,201 cm3 for humans. Yet the two brains contain equivalent regions to Broca's area and Wernicke's area, both of which process language in humans. The neural wiring in chimpanzees is more attuned to quick, direct action; in humans, the same basic wiring is more adapted for higher cognition.

  Chimpanzees occupy a wide stretch of tropical Africa, from dry savanna and swamp forest to montane and evergreen rainforest. At Taï in Ivory Coast, they live in what remains of the country's tropical rain forest. At Bossou in Guinea, they occupy the edges between forest, savanna, and cultivated land. Their communities range from around 15 to more than 150 members, though daily life is spent in much smaller, temporary groups. Males remain in their natal communities for life, while females generally move out at adolescence. That asymmetry has a genetic consequence: males within a community are more likely to be related to each other than females are.

• 4. Politics, Power, and Kinship

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  A dominant male chimpanzee must re-establish his rank every time he rejoins his group. This is a structural feature of fission-fusion society, where individuals constantly break off and reunite. A large amount of aggressive display erupts within five to fifteen minutes after a reunion, as the returning male signals his position. Physical attacks are less common than displays, but the threat of violence underlies every interaction.

  Coalitions govern rank more than raw strength. Males that form alliances can dominate a third individual they could not overpower alone, and politically skilled chimpanzees can exert influence over aggressive interactions regardless of their rank. Low-ranking males frequently switch sides, benefiting from instability because high-ranking rivals become distracted fighting each other. Social grooming binds coalitions together and is more common among adult males than any other pairing in the group.

  A study published in 2010 found that chimpanzee groups wage war over territory rather than mates. Patrols from large groups absorb smaller groups' ranges, gaining access to more food and females. Jane Goodall observed groups of male chimpanzees at Gombe patrolling borders and brutally attacking individuals who had split off from the main community. That said, primatologist Christine Webb, after analysing chimpanzee and bonobo sanctuary communities, concluded that variation within each species is greater than the differences between them. Females also form alliances, and there is at least one recorded case of females collectively securing a dominant position over males, though this occurred in captivity.

  Mothers sit at the centre of a chimpanzee's early world. A chimpanzee's future rank may depend on its mother's status. Orphaned chimpanzees are occasionally adopted by adult males who, by some accounts, become as protective as any mother.

• 5. Tools, Memory, and Laughter

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  Chimpanzees have used stone tools for at least 4,300 years, based on archaeological evidence. A chimpanzee from the Kasakela community was the first nonhuman animal ever recorded making a tool, modifying a twig into an instrument for extracting termites. West African chimpanzees crack open hard nuts with stones or branches, choosing specific stone tools that are kept separate from nut-cracking sites. In Senegal, west African chimpanzees were found to sharpen sticks with their teeth and use them to spear Senegal bushbabies out of holes in trees.

  A 30-year study at Kyoto University's Primate Research Institute showed that chimpanzees can learn to recognise the numbers 1 through 9 and their values. One subject, Ayumu, could correctly recall the positions of jumbled digits flashed onto a screen for less than a quarter of a second, and performed better than human adults in the same test.

  Chimpanzees also pass the mirror self-recognition test, with two young individuals retaining that recognition after a full year without access to mirrors. A 2022 study reported that chimpanzees crushed insects and applied them to their own wounds and to the wounds of other chimpanzees. When group members witness a sudden death, they respond with vocalisations, aggressive displays, and touching of the corpse; mothers have been reported to carry dead infants and groom them for several days.

  Chimpanzee laughter is real but unrecognisable to most humans. It is produced by alternating inhalations and exhalations that sound more like panting than a laugh. Both chimpanzees and humans share the same ticklish areas, including the armpits and belly, and the enjoyment of tickling in chimpanzees does not diminish with age.

• 6. Language at the Boundary

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  Allen and Beatrix Gardner spent 51 months in the 1960s teaching American Sign Language to a chimpanzee named Washoe. By their account, Washoe learned 151 signs and had spontaneously taught some to other chimpanzees, including her adopted son Loulis. Over time, she was reported to have acquired more than 350 signs.

  Herbert Terrace of Columbia University trained a chimpanzee named Nim Chimpsky, the name a deliberate nod to theorist Noam Chomsky. In November 1979, Terrace and psycholinguist Thomas Bever re-examined the videotapes of Nim frame by frame. Their reanalysis concluded that Nim's use of signs could be explained by prompting from experimenters and errors in data reporting. Terrace stated that Nim never initiated conversations, rarely introduced new words, and mostly imitated his human trainers. Nim's word strings also varied in ordering, suggesting he could not produce syntax. His sentences did not grow longer over time, unlike human children whose vocabulary and sentence length increase together. Terrace concluded: "Language still stands as an important definition of the human species."

  Chomsky opposed this conclusion, arguing from his own theory that language capacity is inherited exclusively by humans. David Premack continued to debate the question. The chimpanzee brain contains the structural equivalents of both language-processing regions found in humans, yet whether those structures support anything recognisable as language remains one of the field's most contested questions.

• 7. In Space and in Laboratories

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  Ham, the first great ape in space, launched aboard the Mercury-Redstone 2 capsule on the 31st of January 1961 and survived the suborbital flight. Later that same year, on the 29th of November, Enos became the third primate to orbit Earth, flying on Mercury-Atlas 5 after Soviet cosmonauts Yuri Gagarin and Gherman Titov.

  Back on the ground, hundreds of chimpanzees have spent decades in American research laboratories. Two federally funded centres have been involved: the Yerkes National Primate Research Center at Emory University in Atlanta, Georgia, and the Southwest National Primate Center in San Antonio, Texas. Unlike most laboratory animals, research chimpanzees tend to be used repeatedly over decades, sometimes for up to 40 years.

  In 1996, the US National Institutes of Health imposed a five-year moratorium on breeding chimpanzees for HIV research, extended annually after 2001. A 2007 decision made the moratorium permanent. Five hundred chimpanzees have since been retired from laboratory use and relocated to sanctuaries in the United States or Canada. A recent study suggests that some chimpanzees retired from laboratories exhibit a form of post-traumatic stress disorder. Pascal Gagneux, of the University of California, San Diego, argues that given chimpanzees' sense of self, their use of tools, and their genetic closeness to humans, research using chimpanzees should follow the ethical guidelines applied to human subjects who cannot give consent.

• 8. Survival and Threat

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  Jane Goodall began the first long-term field study of chimpanzees at Gombe Stream National Park in Tanzania in 1960. Her research has continued for more than 60 years, and it was through Goodall that the Kasakela community became the most documented chimpanzee population in the world. In 1966, she witnessed a polio outbreak that killed six out of the seven chimpanzees she was observing in Gombe.

  From an estimated one million individuals in the early 1900s, the wild chimpanzee population has fallen to between roughly 172,700 and 299,700. The IUCN lists the species as endangered. The western chimpanzee, whose range once extended from southern Senegal east to the Niger River, is classified as Critically Endangered, with an estimated 21,300 to 55,600 individuals remaining, concentrated mainly in Guinea, Sierra Leone, and Liberia.

  Habitat destruction drives the decline. Deforestation in West and Central Africa has reduced and fragmented chimpanzee territory. Road construction accelerates that fragmentation and opens access to poachers. In Ivory Coast, chimpanzees make up 1-3% of the bushmeat sold in urban markets. Disease transmission from humans is also a growing threat: chimpanzees are vulnerable to influenza, pneumonia, tuberculosis, Ebola, and the common cold, as Craig Stanford details in Planet Without Apes. As human populations near chimpanzee habitats grow, so does the frequency of contact and the risk of outbreak.

  Goodall has pushed for vaccination programmes to protect vulnerable chimpanzee populations, an approach the Gombe outbreaks helped motivate. The five epidemics she identified since the mid-twentieth century, including that 1966 polio event, point to a specific, preventable category of threat that medical intervention could address.