Humans and chimpanzees share approximately 98.7% of their DNA, having diverged from a common ancestor about 6-7 million years ago, yet they have developed dramatically different lifestyles: chimpanzees remain forest-dwelling primates with complex social structures, tool use, cultural traditions, and sophisticated political behaviors, while humans evolved to live in diverse environments with language, technology, and global spread. Despite these differences, chimpanzees demonstrate remarkable cognitive abilities including self-recognition in mirrors, theory of mind, intentional deception, empathy, grief responses, and complex social learning that challenges traditional boundaries between human and non-human intelligence.
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Welcome. Tonight we are going back. Not forward, not toward the new and the unfamiliar. Not into the strange territories that most of these conversations ask you to enter. Tonight we are going back. Back along the thread that connects you to everything that came before you. Back through the generations and the centuries and the millennia. Back through the evolutionary history that produced the body you are lying in. The brain you're using to hear these words. the nervous system that is even now beginning to release the tension of the day and allow the sleep to approach. We are going back until we reach the place where the thread divides. The branching point where one lineage became two, where the ancestors of the modern human and the ancestors of the modern chimpanzee were still the same animal and then slowly over the pressure of millions of years were not.
We are going to that branching point and then we are going to follow the other branch. The one that did not become us.
The one that stayed in the forest and became what the forest made of it. And we are going to spend this night with the chimpanzee.
Find your position. Let the weight of your body distribute through the surface beneath you. The weight of a primate at rest. The weight of an animal that has been carrying itself through the day in the upright posture that its lineage developed on the African savannah. And that is, if you think about it honestly, still somewhat new in the evolutionary history of apes. Still not quite so refined by millions of years of use as the quadripedal postures of the other great apes. Still occasionally producing the back pain and the knee problems and the compressed spine that are the cost of standing on two legs in a skeleton that was built for four. Let that weight go now. Let the uprightness release. Let the body settle into the horizontal.
That is the body's preferred state for the deepest rest. The posture that the chimpanzeee also adopts in its night nest in the forest canopy. The large body stretched across the bent branches.
The breathing slowing. The day's complexity fading. Your breathing is slowing. The forest is close tonight or it will be in a few minutes. The equatorial forests of West and Central Africa where the chimpanzees have lived for millions of years. the forests of Guinea and Sierra Leon and Ivory Coast and Ghana and Nigeria and Cameroon and Garbon and the Democratic Republic of Congo and Uganda and Tanzania. A range that stretches across the equatorial belt of the continent in a band of tropical forest and woodland and gallery forest that is despite everything that has happened to it in the past century still vast still complex still alive with the sounds and the movements of the animals that make their lives in it. The chimpanzeee is in the trees tonight, as it is every night, having built its night nest as the light failed. The nest in the fork of a tree 10 or 15 or 20 m above the ground. The platform of bent branches covered with leaves that serves as the chimpanzeee's bed, built fresh every evening, abandoned every morning.
The pattern of an animal that does not return to the same sleeping place because returning to the same sleeping place would allow predators to predict where it would be. The chimpanzee pan troglogites.
The species name means cave dweller. A name given by the naturalists who first described the species from specimens rather than from observation. A name that has nothing to do with what chimpanzees actually do, which does not include living in caves. The common name is thought to derive from a bantto language of what is now Angola. The word chimpanzee meaning something like mockery of man or something close to it.
A name given by the people who shared the forest with these animals and who had been living alongside them for their entire human history in that region.
Watching them and interpreting their behavior through the lens of their own experience of what an animal that walks upright and uses its hands to eat and cries when it is frightened and laughs when it plays actually is.
The Bantto speaking peoples of central Africa did not need western science to tell them that the chimpanzee was something different from other animals.
They knew. They had always known. The name they gave it acknowledged the difference. The number first because the number is always the context. There are between 170,000 and 300,000 chimpanzees alive today. The range reflecting the genuine uncertainty in the estimates.
The difficulty of surveying animals that live in dense forest over wide areas and that are present in some locations in small numbers and in others in larger groups and that are in some areas so rarely encountered by humans that their presence can only be inferred from signs rather than from direct observation.
170,000 to 300,000.
In 1900, the estimate is that there were approximately 1 million chimpanzees across the range. In 120 years, the population has declined to somewhere between 17 and 30% of its early 20th century level. A decline produced by habitat loss as the forest is cleared for agriculture and logging, by hunting for bush meat, by the capture of infants for the exotic pet trade and for research purposes, by infectious disease, by the loss of forest connectivity. As the continuous forest is fragmented into isolated patches that support isolated populations unable to exchange individuals and maintain the genetic diversity that isolated populations need to survive in the long term. The decline is continuing. The chimpanzeee is listed as endangered on the IUCN red list, a step below critically endangered on the assessment framework. But the trajectory in most parts of the range is downward, and the rate of habitat loss has not slowed significantly in most countries where chimpanzees live. The number tonight is somewhere between 170,000 and 300,000.
The number a 100 years from now depends on decisions that have not been made yet. Actions that have not been taken yet by governments and communities and conservation organizations and the broader human world. That is the context in which the chimpanzees future will be determined. Hold that context lightly.
We are not here tonight to carry the weight of the conservation crisis into the sleep. We are here to know the chimpanzeee to understand what it is and what it does and what its existence represents because knowledge is the foundation of the concern that produces the action that changes the number. We are here to meet the animal. The rest follows the relationship. The chimpanzeee and the human share approximately 98.7% of their DNA. That is closer than the gorilla, closer than the orangutan, closer than any other living species.
The genetic distance between a chimpanzeee and a human is smaller than the genetic distance between a chimpanzeee and a gorilla. Smaller than the distance between a dog and a fox, smaller than the distance between a horse and a zebra. The chimpanzeee is not our closest living relative. It is our sibling in the evolutionary sense.
Two lineages from the same immediate ancestor diverged approximately 6 to 7 million years ago in a process whose details are still debated but whose outcome is the two species that exist today. 6 to 7 million years of separate evolutionary history has produced bodies and brains and behaviors that are substantially different. But the foundation beneath those differences is the same. The same genetic code, the same fundamental cellular machinery, the same neurotransmitters and hormones and immune system proteins, the same basic architecture of the nervous system, the same capacity for suffering and joy and social attachment, and the grief that follows loss. 6 to 7 million years. The lineage that became the chimpanzeee and the lineage that became the human were the same lineage when the Mediterranean Sea last dried up completely. When the first hominins were beginning the experiments with upright walking in the African woodland, when most of the mountain ranges of the modern world were already as tall as they would ever be.
In 6 to 7 million years, the chimpanzeee lineage has remained in the forest and become what the forest made of it. The human lineage has moved out of the forest into the woodland and then the savannah and then has spread across every continent and modified the earth's atmosphere and sent objects beyond the solar system. 6 to 7 million years, two very different journeys from the same starting point. Close your eyes now or let them soften in the dark. The forest is around you or will be in a moment.
The chimpanzeee is somewhere above us in the canopy in its night nest, already asleep or settling into sleep. The day's extraordinary activity suspended for the hours of darkness that the forest provides. We are going to spend this night following the chimpanzee through its world, beginning in the morning when the group wakes and descends from the trees, moving through the day with its feeding and its social complexity and its politics and its play and its hunting and its grooming and its conflicts and its reconciliations and ending here in the night in the nest in the quiet of the forest at its deepest hour. We are going to learn what the chimpanzeee is, which turns out to be the most complicated answer that the natural world provides to the question of what an animal is.
The morning the forest begins to lighten and the chimpanzees in the group begin to stir. The first sounds of the day are the rustling of the nest vegetation as the animals move, the occasional soft pant or grunt of waking, and then as the light increases and other groups in the area begin their own waking. The long call, the pant hoot that is the chimpanzeee's signature vocalization.
The call that announces presence and identity and social status. the call that travels through the forest for kilometers and that every chimpanzee in the region responds to by updating its mental map of who is where and what the social landscape of the morning looks like. The pant hoot begins with a series of soft hoots that accelerate in pace and volume, building through a scream phase to the climax of the call. A powerful series of barks that carry the individual's identity in the specific pattern of their production. The chimpanzeee's voice print recognizable to every other chimpanzeee in the community as this individual and no other. The community. The chimpanzeee does not live in a simple group of the kind that the gorilla lives in. A single silverback and his females and their offspring. The chimpanzeee lives in a fish and fusion community, a social organization of remarkable flexibility in which the community as a whole may contain 20 to 150 individuals who share a common territory but who move through that territory in smaller subgroups, parties of varying composition that form and dissolve over the course of hours and days. The individuals within the community associating in constantly changing combinations depending on the food distribution, the social relationships, the reproductive state of the females, the political dynamics of the male hierarchy, and factors that are not always apparent to human observers.
The chimpanzeee community is a social system of extraordinary complexity. A network of relationships maintained across time and distance where every individual knows every other individual and has a specific relationship with each of them. A relationship with a history with debts and obligations and affiliations and antagonisms accumulated over years of shared life in the same forest. The alpha male, the top of the male dominance hierarchy of the chimpanzeee community. The individual who has successfully competed his way to the position of dominant male and who maintains that position through a combination of physical capability, political alliance and the management of the coalitions that are the currency of chimpanzee power politics. The alpha male of a chimpanzeee community is not necessarily the largest or the strongest individual. He is the individual who is best at building and maintaining the alliances that determine the outcome of the political competition. He is the individual who knows which males to support and which to oppose. Who understands the social dynamics well enough to intervene in the right conflicts on the right side, who can manage the contradictory demands of different allies without alienating the coalitions he depends on. The alpha male of a chimpanzeee community is a politician. He is managing a constituency. He is doing what politicians do, which is to navigate a complex social environment where power depends not on individual capability alone, but on the support of others who can be gained or lost through the accumulated choices of daily social interaction. Jane Goodall arrived at Gome in 1960 with almost no prior field experience and a brief from Louis Leaky to observe chimpanzees in their natural habitat and to stay long enough to see what could not be seen quickly. She stayed for 60 years. What she found in those first years, the findings that sent her name around the world and that changed the way we think about what an animal can be were things that no scientist had expected to find in any nonhuman animal. The chimpanzees at Gomebe were making and using tools. They were stripping leaves from twigs to create probes that they inserted into termite mounds to extract the termites that they ate. When Goodall reported this to Leaky by Telegram, he famously replied that we must now redefine tool, redefine man, or accept chimpanzees as humans. Leaky was right that the finding required a redefinition. and the redefinition that has been happening ever since in the study of animal cognition driven by Goodall's work and by the decades of research at Gome and at other chimpanzeee study sites that followed it gives a redefinition not of the chimpanzee but of what we thought an animal was and what we thought a human was and where the boundary between the two lies which turns out to be much less clear and much less absolute than the pregbe world believed the tools Termite fishing is one tool use among many that chimpanzees have been documented engaging in across their range. Chimpanzees in West Africa use stone hammers and stone anvils to crack nuts, a technology that has been observed to be transmitted within communities as a cultural practice.
Young chimpanzees learning to crack nuts by watching their mothers and other adults and then practicing the skill over the years of childhood until they have mastered the specific combination of technique and force that produces a cracked nut rather than a shattered one or an uncracked one. The nut cracking is not present in all chimpanzeee populations. It is present in some populations in West Africa and absent in populations that have the same species of nuts available to them but do not crack them. It is a technology, not an instinct. It is something that has been invented perhaps multiple times and that is transmitted through social learning within the communities that have it.
Chimpanzees in the Thai forest of Ivory Coast use leaf sponges to extract water from tree cavities they cannot reach with their mouths, crumpling leaves to create an absorbent wad that they dip in the water and suck. Chimpanzees in Uganda have been observed using sticks to probe and extract honey from bee nests in sequences that involve multiple different tools used in a specific order. The most complex tool using sequence observed in any wild chimpanzeee population, a multi-step technological process that requires planning and the sequencing of different actions toward a delayed goal.
Chimpanzees use stones as projectiles, throwing them at rivals and at predators with an accuracy and a force that reflects a throwing ability that is not far behind the humans. The same basic biomechanics operating in a body that is in the relevant dimensions not dramatically different from the human throwing body. The chimpanzees toolkit is not as large or as varied as the humans, but it exists. It is real. It is transmitted culturally between individuals and across generations. And it represents a form of technology in the strict sense of the word. The use of material objects as tools to accomplish tasks that the body alone cannot accomplish. The culture. The tool use is one expression of a larger phenomenon that researchers have called chimpanzeee culture. The presence in chimpanzeee communities of behavioral traditions that vary between communities in ways that cannot be explained by ecological differences alone. Traditions that are present in some communities and absent in others that live in similar habitats.
Traditions that appear to be transmitted through social learning from individual to individual and from generation to generation in the same way that human cultural practices are transmitted. The comparison of behavioral data across the seven longestrunn chimpanzeee study sites in Africa conducted in a landmark study published in 1999 identified 39 behavioral patterns that were customary or habitual in at least one community and absent in at least one other. Patterns that varied between communities in the way that cultural practices vary between human communities. each community having a subset of the behaviors that any chimpanzeee could learn and maintain.
The 1999 study was the formal declaration that chimpanzees have culture in the scientific sense and it shifted the framework within which all subsequent research on chimpanzeee behavior has been conducted. Let your breathing slow now. The forest is around us and the morning is underway. The parties forming and beginning to move through the forest in search of the fruit that will occupy most of the day.
The chimpanzees move through the forest with a speed and an efficiency that reflects years of intimate knowledge of the specific trees in their territory.
The mental map that each individual maintains of which trees are fruing, which are ripe, which have been visited recently and are likely to be depleted, which offer the specific food that is most desirable at this moment of the day.
The chimpanzees foraging is not random.
It is planned or it has the functional equivalent of planning. The individual rooting its movement through the forest toward the resources it has learned to expect in specific locations at specific times of year using a cognitive map of the territory that is detailed and accurate and maintained through continuous updating as the forest's fruiting patterns change across the seasons. The chimpanzees diet is extraordinarily varied. Fruit is the dietary staple when available. Providing the high calorie food that fuels the chimpanzees active and metabolically demanding life and the distribution of fruing trees across the territory is the primary driver of the fish and fusion dynamics. The parties coalescing at productive trees and dispersing when the trees are depleted. But the chimpanzee also eats leaves and flowers and bark and seeds and insects and honey opportunistically whenever these foods are available. and worth the energy of acquiring them. And the chimpanzeee hunts. The hunting of the chimpanzeee is one of the most behaviorally complex and most socially significant activities in the chimpanzeee's repertoire and it requires extended attention. The hunt the hunting of red colibus monkeys by chimpanzees at Gomebe and at the Thai forest and at other study sites has been documented in detail over decades. And what the documentation reveals is a hunting behavior that is organized, coordinated, persistent, and socially embedded in ways that were not expected in any non-human animal. The chimpanzeee hunt begins with the detection of a colibus group. And when one individual begins to move toward the colibus, others join. The party composition shifting to include the males who are the primary hunters. The hunters approach the colibus group in a way that is not a simple convergence of individuals on the same prey, but a division of roles. Some individuals driving the colibus through the canopy while others take blocking positions ahead of the projected escape routes, cutting off the retreat and directing the colibus toward the location where other hunters are waiting. The coordination is not perfect. It does not always achieve its apparent goal, and the degree to which it reflects genuine intention and planning rather than the simultaneous response of multiple individuals to the same stimuli is still debated by researchers, but the outcomes are consistent with coordination. The success rates of multi-individual chimpanzee hunts are higher than the success rates of single individual hunts. The presence of more hunters in more positions produces more successful captures.
The social organization of the hunt produces better results than individual hunting would produce. When a hunt succeeds, the carcass is shared, not equally, not randomly, but in patterns that reflect the social relationships of the individuals present and the political dynamics of the moment.
The alpha male typically controls access to the carcass, tearing pieces from it and distributing them to individuals he chooses, keeping the largest share for himself, sharing with allies, withholding from rivals, using the meat as a social currency in the ongoing management of the political relationships that maintain his position. Females in estrus, showing the sexual swelling that signals their fertility, receive meat more often than females not in estrus. A pattern that reflects the male's use of food sharing as a reproductive strategy. Individuals who participated in the hunt receive shares more often than those who did not. A pattern that suggests something like reciprocal exchange, something like the expectation that contribution is rewarded. A social logic that is one of the foundations of human economic behavior applied in the context of a chimpanzeee hunting party.
The politics. The chimpanzee community has a political life. And this is not a metaphor or an anthropomorphization.
It is a precise description of a set of behaviors that match the definition of political behavior. the competition for power and influence within a social group through the management of alliances and coalitions rather than through individual dominance alone.
France Deval who spent years observing the chimpanzeee colony at Arnam Zoo in the Netherlands and who published his observations in the 1982 book chimpanzeee politics documented in detail the strategies that the chimpanzees used to gain and maintain social position. Strategies that included the formation of coalitions between lower ranking males to displace a dominant male, the use of sexual access to females as a currency of alliance, the targeting of an alpha male's key allies rather than the alpha male himself in order to undermine his support base before directly challenging him. and the reconciliation behaviors that followed conflicts, the grooming and the reassurance contact that repaired relationships damaged by competition and that maintained the social fabric of the group through the inevitable conflicts of political life.
Dval's analysis of the Arnum chimpanzeee politics was met with significant resistance when it was published because the comparison with human political behavior was too direct, too specific, too detailed to be comfortable. The resistance has faded as the evidence has accumulated. The chimpanzee does politics. The chimpanzeee does it without language, without written laws, without institutions, but with the same fundamental logic. The logic of coalition, the logic of alliance, the logic of using relationships with others to acquire and maintain power within a social group. The deception. One of the most significant and most discussed findings from the decades of chimpanzeee research is the evidence of intentional deception. The ability to produce behavior that is designed to create a false belief in the mind of another individual. Deception requires theory of mind. The ability to model the mental states of others to understand that another individual has beliefs and that those beliefs can be different from reality and that behavior can be directed at influencing those beliefs.
At Arnham, Dval observed a subordinate male who was displaying to a dominant male successfully suppressed the screaming that typically accompanied display. Apparently, to avoid attracting the dominant male's attention to the display, a suppression of a normally automatic response that implies the ability to model the dominant male's awareness and to act on that model. At Gomebe and at other field sites, researchers have documented chimpanzees concealing their food from other individuals by blocking access with their bodies or by moving away from other individuals before beginning to eat. Concealment behaviors that imply an awareness of other individuals access to information and an active strategy of manipulating that access. The evidence for chimpanzee theory of mind. The evidence that chimpanzees understand that other individuals have mental states and that those states can be influenced is substantial and continues to grow. The reconciliation after conflicts chimpanzees reconcile.
This observation also first documented in detail by Dval established that chimpanzees do not simply fight and then resume normal relations without any specific behavior directed at repairing the relationship. They approach the former opponent, often within minutes of the conflict's end, and they make contact, embracing, kissing, grooming, the specific behaviors that in chimpanzzeee communication signal friendly intent and reassurance. The reconciliation reduces the tension that follows a conflict and repairs the relationship between individuals whose long-term social collaboration is more valuable than the short-term gain of the conflict. The chimpanzeee reconciles because it lives in a world where long-term relationships have value, where today's opponent may be tomorrow's ally, where the management of social relationships over time is more important than the outcome of any single interaction. This is the same logic that produces reconciliation in human social life. The same understanding that relationships have long-term value that exceeds the short-term value of maintaining grievances. And it operates in the chimpanzee through the same neural architecture, the same emotional substrate that it operates through in the human, the empathy. The chimpanzee demonstrates behaviors that are consistent with empathy, the capacity to perceive and respond to the emotional states of others. Chimpanzees comfort distressed individuals, approaching individuals who have been involved in conflicts or who are vocalizing distress and making contact with them, providing the physical reassurance that reduces the distress signals. The comforting behavior is not random. It is preferentially directed toward individuals who are close affiliates of the comforting individual, toward family members, and toward individuals with whom the comforter has a strong bond.
The selectivity reflecting the same pattern that human empathy shows, the tendency to respond more strongly to the distress of those who are close to us.
Chimpanzees have been observed consoling individuals who have just lost a high-ranking position in the dominance hierarchy, approaching the defeated male and making contact in a context where there is no direct benefit to the comforter from the interaction.
Chimpanzees have been observed grieving.
Mothers have been observed carrying their dead infants for days, refusing to put the body down. The behavior clearly not serving any adaptive function, but clearly reflecting an emotional response to the loss that has a duration and an intensity that the word grief, if we use it carefully and without overclaiming, seems to capture. The grief, the chimpanzees response to the death of a close social partner, has been documented at multiple study sites and in captive groups. And the documentation is consistent enough to support the conclusion that chimpanzees experience something that functions like grief. The pattern is specific. Reduced activity and appetite following the death of a close associate. Increased time spent near the body of the deceased in the hours immediately after death.
Vocalizations that are different from normal vocalizations in their frequency and character. And the lingering behavioral effects that persist for weeks or months after the death. At Gomebe, following the deaths of individuals who had been central figures in the community, the behavioral changes in the surviving community members were measurable and prolonged. The males who had been allied with the deceased alpha male showed changes in their ranging patterns and their association patterns for months after the death. The juveniles who had lost their mothers showed behavioral disruptions that in some cases contributed to their own deaths from the failure to thrive that sometimes follows the loss of the maternal relationship in species that depend on long-term maternal investment.
The infant chimpanzeee and its mother.
And the bond between a chimpanzeee infant and its mother is the most important relationship in the infant's life and one of the most important relationships in the mother's life. A bond that begins at birth and that persists through the infant's entire development. The mother carrying the infant for the first year of its life, nursing it for 3 to 5 years, maintaining close association with it for a decade or more after weaning. The infant chimpanzeee is born helpless in the way of all great ape infants. Unable to support its own weight, unable to cling independently for the first weeks of life, completely dependent on the mother for warmth and nutrition and protection, and the physical contact that is for the great ape infant, not a luxury, but a physiological necessity, the absence of which produces measurable stress and developmental disruption. The infant that is adequately held and nursed and carried and interacted with by its mother develops normally. The infant that loses its mother in early life or that is raised without adequate maternal contact shows developmental disruptions that persist into adulthood. The social and emotional architecture of the individual shaped by the quality of the early relationship in ways that echo with uncomfortable familiarity the research on the effects of early attachment in human development. The mother's investment. A female chimpanzeee in the wild produces approximately five offspring in her lifetime if she lives to old age which in the wild means 30 to 40 years. Each offspring requires four to 5 years of nursing during which time the mother does not conceive again. Each offspring requires years of close maternal supervision and support. Each offspring represents an investment that is by the standards of most mammals enormous. the long gestation and the extended nursing and the prolonged juvenile dependency adding up to a reproductive investment per offspring that is rivaled in the animal kingdom only by the other great apes and by humans.
This investment means that the loss of any offspring is significant that the loss of an offspring to predation or disease or infanticide is a reproductive cost that cannot be quickly recovered.
And it means that the mother's vigilance and her protection of her infant are not simply behavioral tendencies but the expression of an enormous biological investment whose value drives the strength of the maternal bond. The infant growing the chimpanzeee infant develops faster than the human infant in some respects, slower in others. The developmental trajectory of the great apes sitting between the accelerated development of monkeys and the extended development of humans in a comparative developmental sequence that reflects the evolutionary trajectory of the great ape lineage toward longer childhoods and greater learning periods. The infant chimpanzee is riding on its mother's back by 3 months, beginning to venture short distances from her by 6 months, beginning to play with other infants by 8 months, beginning the long process of learning the social skills and the ecological knowledge and the technological capabilities that adult life in the chimpanzeee community requires. The mother is the primary teacher not through formal instruction but through the provision of opportunity and the model of adult behavior that the infant observes and attempts to reproduce and through the specific behavior of active teaching that has been documented in the nutcracking communities where mothers place nuts on anvils within their infants reach and allow the infants to attempt the cracking occasionally demonstrating the correct technique by taking the hammer and showing the movement. the learning of the community's behavioral traditions. The chimpanzeee infant does not arrive in the world pre-equipped with the specific behaviors of its community. It arrives pre-equipped with the capacity to learn those behaviors, the neural architecture for social learning, the tendency to attend to the behaviors of individuals it is close to, the motivation to imitate and to practice what it observes, the specific behavioral traditions of the community, the specific tool types and the specific grooming gestures and the specific communicative conventions that are characteristic of this community and not of another are acquired through years of immersed observation in the social environment of the community. Learned from the mother and from the other individuals in the community in the way that cultural practices are learned through participation and observation and imitation and the social feedback that corrects errors and reinforces successful performance. The chimpanzeee infant is born into a culture and acquires that culture through the same mechanisms that human infants acquire the cultures they are born into. The universal processes of social learning operating through the particular content of the specific community's traditions.
Breathe slowly. The forest is in full morning activity around us, and the parties are moving through the canopy and along the ground and through the understory in search of the fruit that will occupy the next several hours. And the forest is full of the sounds of the chimpanzeee community going about its day. The calls and the vocalizations of individuals locating each other and announcing their position and responding to the pan hoots of distant community members and the alarm calls of nearby individuals who have detected something worth attending to. The forest is not quiet. The chimpanzee makes the forest loud, filling it with the acoustic signatures of its complex social life.
The drumming on the buttress roots of large trees that carries as far as the pant hoot and that serves similar functions of long range communication.
The play screams of juveniles. The soft grunts of individuals who are close together and feeding. The food calls that bring distant community members to productive trees. The begging sounds of subordinate individuals trying to get access to food that a dominant individual is controlling. The drumming.
When a chimpanzeee arrives at a large tree with prominent buttress roots, the flanges of wood that radiate from the base of the trunk in the way that large rainforest trees grow, it may drum, hitting the buttress roots repeatedly with its feet in a behavior that produces a resonant boom that carries through the forest for hundreds of meters. The drumming is a long range communication and the pattern of the drumming. The number of bouts and the intervals between them carries information about the identity of the drummer and about the direction of travel.
Other chimpanzees in the community respond to drumming from community members by updating their assessment of where that individual is and where it is going and sometimes by moving toward the drummer or by drumming in response from their own location. A long range conversation between individuals who are too far apart to see each other or to hear each other's quieter vocalizations, coordinating their movements through the forest through the acoustic channel that the buttress roots provide. The chimpanzees drumming is its long-distance telephone, its way of maintaining contact with the community across the distances that the fish and fusion social system creates. the female chimpanzeee in the community. The social organization of the chimpanzeee community is marketkedly different in its treatment of the two sexes from the gorilla's social structure. In the chimpanzeee, it is the males who are filatric remaining in the community they were born into for their entire lives.
While females typically immigrate at puberty, transferring to neighboring communities and establishing themselves there as new members of a community to which they were not born. The males of the community are therefore related to each other, bound together by kinship as well as by the social relationships of their shared adult lives, while the females are unrelated immigrants who have had to establish themselves in a community of strangers. The male chimpanzees patrol their territory together. The related males of the community cooperating in the defense of the range against neighboring communities in behavior that has significant and disturbing parallels to patterns of intergroup violence in human societies. The patrols, the boundary patrols of the chimpanzeee community are among the most discussed and most contested findings in the literature on chimpanzee behavior. The males of a community periodically form parties, sometimes including females, that move to the edges of the community's range, and then travel along the boundary in a distinctive manner, moving slowly and silently, stopping to listen and to smell, avoiding the vocalizations that characterize their normal movement through the forest, attending to the signs of neighboring community members in the area. When they encounter members of the neighboring community in small numbers or as isolated individuals, they sometimes attack them with a ferocity and a persistence that is unlike their intracom community aggression. The attacks sometimes resulting in the death of the attacked individual. Over years at Gomebe, Goodall and her colleagues documented what came to be called the Four Years War, a period of systematic lethal raiding by the Kasaka community against the Kahama community, which eventually resulted in the killing or disappearance of every male in the Kahama community and the absorption of the Kahama females and their range into the Casakila territory. The documentation of this behavior provoked intense debate about what it implied about the origins of human violence. A debate that has not been resolved and that touches on some of the deepest and most difficult questions about what the human capacity for lethal intergroup violence represents in the context of our evolutionary history.
What the chimpanzees intercom community violence does and does not imply about human violence is a question that requires careful thought. more careful thought than either the position that says the chimpanzees behavior demonstrates that human violence is natural and therefore inevitable or the position that says the chimpanzees behavior is irrelevant to understanding human violence because humans are different. Both of these positions are wrong in ways that are worth understanding. The chimpanzeee is not a simple model for human behavior. It is an animal with its own specific social system and its own specific ecological pressures and its own specific evolutionary history. And the behaviors it exhibits, including the lethal intercom community violence, are products of that specific history and not direct homalues of any human behavior. But the chimpanzeee is also our closest living relative. And the behaviors it exhibits are the behaviors of an animal that shares 98.7% of our DNA. and that operates through essentially the same neural architecture. And the study of those behaviors in the context of chimpanzeee ecology and chimpanzeee social life does provide information about the conditions under which lethal intergroup violence emerges and the proximate mechanisms through which it is organized.
Information that is not irrelevant to the study of human violence, even if the relationship between the two is complex and non-deterministic.
The bonobo comparison returns here because the bonobo paniscus, the chimpanzees closest relative and the species that shares with the chimpanzee, the distinction of being the human's closest living relative, does not conduct lethal intercom community raids.
The bonobo lives south of the Congo River in a forest that is more continuously productive than the forests north of the river where the chimpanzeee lives and the different ecology appears to be related to the different social organization. The bonobo's female- centered social system and its use of sexual behavior as a mechanism of social tension reduction producing a community in which lethal intergroup violence has not been observed despite decades of observation at multiple study sites. The comparison between the chimpanzeee and the bonobo is among the most instructive in all of comparative primatology. two species from the same immediate ancestor, separated by the Congo River and by the different ecologies on each side of it, having evolved substantially different social systems that produce substantially different patterns of behavior. A natural experiment that speaks to the plasticity of social organization and the influence of ecological conditions on the forms that social life takes. The communication of the chimpanzee. The chimpanzeee does not have language. This needs to be said carefully and precisely because the decades of language research with captive great apes have produced a literature full of claims that are contested and counter claims that are also contested and the question of what the chimpanzee communicates and through what means is genuinely complex and genuinely unresolved at its edges. What is clear is that the chimpanzee does not have language in the sense that humans have language. the capacity for open-ended combinatorial communication using arbitrary symbols with specific meanings that can be combined according to grammatical rules to produce an unlimited range of propositions about the world. The chimpanzee does not produce sentences. It does not have grammar. It does not combine symbols to produce statements that refer to absent objects or past events or future contingencies in the way that language does. The captive chimpanzees who were taught sign language or symbol boards or computer lexograms demonstrated remarkable abilities to use the symbols they were taught to associate them with their reference to use them in requests and in responses to questions and occasionally to combine them in ways that seemed creative and novel. But the accumulated evidence from decades of research suggests that these abilities, impressive as they are, do not constitute language in the full sense.
that they represent something more limited and more contextually bound than the syntactically structured, propositionally rich communication that language is. What the chimpanzee does have and what it uses in the wild with a richness and a complexity that the captive language research did not capture is a gestural and vocal communication system of considerable sophistication.
The chimpanzeee uses hand gestures produced intentionally and directed specifically at particular other individuals to communicate requests and responses and social signals that are understood by the recipient. A chimpanzeee that wants another individual to move will stretch an arm toward it with an open hand. The same gesture that humans use to indicate that someone should come closer. A chimpanzee that wants to groom another individual will scratch its own arm or back at the spot it once groomed, directing the other individual's attention to the location. A chimpanzee that wants play to begin will place its hand on the potential play partner in a way that is recognizably an invitation. These gestures are intentional in the sense that they are directed at specific individuals, that they are persisted in if the initial attempt does not produce the desired response, and that they cease when the desired response occurs.
They are not automatic. They are communicative in the technical sense, acts designed to alter the behavior of another individual by influencing its mental state, the understanding of other minds. The question of whether chimpanzees understand that other individuals have minds, have beliefs and desires and intentions that are different from their own. The question of chimpanzee theory of mind has been the subject of research and debate since David Primac and Guy Woodruff published their famous 1978 paper asking the question, does the chimpanzee have a theory of mind? Primac and Woodruff's initial research with the captive chimpanzeee Sarah suggested that she could attribute intentions to humans.
And the decades of research since then have accumulated evidence that chimpanzees do understand something about the mental states of others. That they distinguish between what they themselves know and what another individual knows. That they can use this distinction in their behavior. directing requests to individuals they know have information about the location of food rather than to individuals they know do not have this information. The evidence is not as clean as the research on human theory of mind and the debates about the interpretation of specific experiments continue. But the weight of the evidence is that chimpanzees have something that functions like a theory of mind. An understanding of other individuals as agents with beliefs and desires that can be different from one's own. An understanding that allows them to anticipate and to influence the mental states of others in the ways that their social and political life requires. The chimpanzees memory. The chimpanzees memory for specific past events, for the specific individuals it has interacted with, and the specific nature of those interactions, is a functional memory, a memory that influences current behavior in ways that imply the retention of specific episodelike representations of past experience. A chimpanzee that was aided by another individual in a conflict will subsequently groom that individual more than its base rate of grooming would predict. the behavior reflecting the memory of the specific past interaction and the reciprocal response that the social logic of the community produces. A chimpanzeee that was attacked by a specific individual will subsequently avoid that individual or behave defensively toward it in ways that reflect the memory of the specific attack. The chimpanzees social life with its complex web of specific relationships maintained over years and decades could not function without the ability to remember specific past interactions with specific individuals and to use those memories in the management of current relationships. The remarkable memory experiment. The Japanese researcher Tetssuru Matsuawa and his colleagues at the primate research institute at Kyoto University have conducted decades of cognitive research with the chimpanzeee II and her son Aayumu that has produced some of the most startling findings in the literature on animal cognition. The finding that attracted the most attention and that has been the subject of considerable research, replication and discussion is the performance of Aayumu and other young chimpanzees on a working memory task in which numbers appeared on a computer screen for a fraction of a second and were then replaced by white squares and the chimpanzee was required to touch the squares in the order in which the numbers had appeared. Hayumu and the other young chimpanzees tested performed this task at a level of accuracy that exceeded the performance of adult humans who were tested on the same task and they performed it faster. The numbers appearing on screen for durations as short as a fifth of a second without significant reduction in accuracy. The finding was replicated and extended in subsequent research, and it remains one of the most discussed examples of a specific cognitive capacity in which the chimpanzeee appears to exceed the human.
A reminder that the cognitive comparison between the two species is not a simple hierarchy with humans at the top, but a complex profile of different capabilities adapted to different demands. and that the chimpanzees specific cognitive strengths reflect the specific demands of its specific life in its specific environment.
The afternoon rest. After the morning's foraging, as the heat builds in the forest and the fruit becomes harder to find as the most productive trees are depleted, the chimpanzeee community tends toward a midday rest. The parties that have been moving and feeding through the morning, settling into a period of reduced activity, grooming and resting and play, the social fabric of the community being maintained and renewed in the quieter hours of the early afternoon.
The grooming pairs settle into their long sessions, one individual parting the fur of another with careful fingers, picking out the parasites and the debris, and occasionally apparently just grooming. Because the physical contact and the social interaction of grooming is intrinsically rewarding in the way that physical contact and social interaction are intrinsically rewarding in social primates. The juveniles play with the focused energy of young animals who have energy to spare. and social skills to develop the play providing the practice for the adult behaviors that will be needed later. The wrestling and the chasing and the object play and the social play with other individuals. All of it building the physical capabilities and the social knowledge that adult chimpanzeee life requires. The grooming in the chimpanzeee as in all the great apes and in humans grooming is the primary currency of social affiliation.
the physical act that maintains the bonds between individuals and that signals the nature and the strength of those bonds to the individuals involved and to the observers around them.
Chimpanzees spend more time grooming than any other great ape. The grooming sessions sometimes extending for an hour or more between closely bonded individuals. The physical contact and the social attention of the grooming functioning as a form of social bonding that has been described by the anthropologist Robin Dunbar as the primate equivalent of human conversation. The extended social interaction that builds and maintains the bonds that make social life possible. Dunbar's social brain hypothesis proposes that the large brains of primates including humans evolved in the context of the demands of managing complex social relationships and that the capacity for language in humans is a development from the grooming behavior of the primate ancestors. language being a more efficient way of conducting the social bonding that grooming provides, allowing the same bonding effect to be achieved simultaneously with multiple individuals rather than only with the one individual who can be groomed at a time. The language hypothesis is speculative and contested, but the underlying observation about grooming and social bonding in chimpanzees is not. The grooming data from long-term chimpanzeee study sites consistently show that grooming time is disproportionately allocated to high-v valueue social partners. That grooming exchanges are more reciprocal between closely bonded individuals and that disruptions to grooming relationships through the death or immigration of a key partner produce measurable social disruption in the remaining individuals.
Grooming is not incidental to chimpanzeee social life. It is the mechanism through which social life is built and maintained. The daily physical activity that keeps the community's social structure intact. The evening, the afternoon feeds and the evening feeds take the parties through the forest as the heat begins to decline and the productivity of the feeding increases again. The chimpanzees moving toward the trees where the most reliable sources of fruit are located in the late afternoon. The individuals calling across the forest to maintain contact and to advertise the direction of their travel. The fish and fusion dynamics of the day playing out in the last hours of light as some parties converge on the same productive trees and others continue their separate ranging. As the light fails, the chimpanzees begin to move toward their sleeping trees. The same trees or the same area of trees that the community has used consistently. The choice of sleeping tree reflecting both the security of the location and the proximity to food resources that will be needed in the morning. The nest building. Each individual builds its own nest. The mother builds hers and the infant sleeps in it with her. The juveniles old enough to sleep alone build their own small nests near the mother. The adult males build in the high canopy 15 to 30 m above the ground. The height providing protection from the leopard. the primary predator of chimpanzees which hunts at night and which rarely climbs to the heights the chimpanzees prefer for sleeping. The nest is built by bending large branches toward a central support and weaving smaller branches and leafy twigs into the platform. The construction taking approximately 5 minutes in an experienced adult and producing a sleeping platform that is both stable and adequately comfortable for the night.
The chimpanzeee does not bring objects to the nest site. It uses what is available at the nest tree which it selects partly on the basis of the suitability of the branch structure for nest construction. The nest is functional and temporary and efficient.
It is also new every evening, a fresh bed every night. And the chimpanzeee that has spent the day building political alliances and managing social relationships and finding and extracting food and vocalizing and grooming and playing and traveling through the forest ends its day in a fresh structure of its own construction. The last act of each day being the creation of the place of sleep. The night descends in the forest quickly. The canopy blocking the last light in minutes once the sun is low enough. The forest going from dim to dark in the time it takes to build a nest. The sounds of the day animals giving way to the sounds of the night.
The nocturnal insects taking over from the dal birds. The frogs beginning their chorus. The occasional call of an owl or a night jar. The sounds that the chimpanzeee has fallen asleep to every night of its life and that carry in their specific combination. The acoustic signature of the specific forest, the known place, the safe place, the home.
The chimpanzeee in its nest, in its tree, in its forest is exactly where it belongs. In the place that its community has used, and in the way that its species has slept since long before there were human observers to watch it, since long before there were humans at all. The chimpanzee's body, the physical reality of what the chimpanzeee is. An adult male chimpanzeee in the wild weighs between 40 and 60 kg, roughly the weight of a small human adult, but the weight is distributed very differently from the human distribution. The chimpanzees upper body massively more muscular in proportion to its body weight than any human. The arms disproportionately long relative to the legs, the hands wide and powerful. The grip strength of an adult chimpanzee approximately three to five times the grip strength of a strong human adult.
The chimpanzees physical power is a feature of its forested environment. The requirement to move through the canopy, to hang from branches, to climb trees, and to swing between them, having produced a body whose upper body strength is developed to a degree that no human body achieves. The chimpanzeee can brachiate, swing hand overhand through the canopy with an agility and a speed that no human observer sees without being immediately aware that this is an environment in which the human is at a significant disadvantage and the chimpanzee is completely at home. The chimpanzees face. The face of the chimpanzeee is the most immediately recognizable non-human face in the world. The face that every child knows from picture books before they have ever seen a live chimpanzee. The wide flat features and the protruding jaw and the prominent brow and the large ears set to the sides of the skull. The face that is recognizably of the same type as the human face and yet clearly different.
The same type in the placement of the features and in the expressiveness of the musculature. different in the proportions and in the specific features that are the products of the specific evolutionary history of the two lineages.
The chimpanzeee's face is expressive, capable of producing a range of emotional expressions that are functionally similar to the expressions of human faces. The relaxed open mouth of play, the compressed lips and the averted gaze of submission, the forward and upward expression of excitement, the wide eyes and the exposed teeth of fear or aggression. The facial expressions of the chimpanzee are legible to humans without any training. the basic emotion categories that they represent being sufficiently similar to the emotion categories of human facial expressions that the reading of chimpanzeee faces is not something that requires specialized knowledge to attempt the chimpanzee and the mirror. The mirror test the test of self-recognition in which an animal is marked with a spot of paint while sedated and then observed upon waking to see whether it uses the mirror to inspect the mark on its own body. a behavior that indicates that the animal recognizes the mirror image as itself rather than as another individual. The chimpanzee passes this test. Not every chimpanzeee and not every time, but the pattern across multiple studies is clear enough to establish that chimpanzees have the capacity for self-recognition in mirrors that has been used as a marker of self-awareness since Gordon Gallup Jr. first tested the behavior in chimpanzees in 1970. The finding that chimpanzees recognize themselves in mirrors placed them in a very small category of animals, joined subsequently by the other great apes, by elephants, by bottl-nose dolphins, by orcas, and by a few other species, a category that was before 1970 thought to be exclusive to humans. The implications of the finding for our understanding of the chimpanzees inner life and its self-awareness have been discussed for 50 years and continue to be discussed. The question of what self-recognition in a mirror actually indicates about the underlying cognitive and phenomenal states of the animal that performs it being a genuinely difficult philosophical and empirical question.
The aging chimpanzee, an old chimpanzee in the wild or in captivity is a striking animal to observe. The body's power diminished by the decades of intense physical life.
The face marked by the injuries and the social experiences of a life lived in the competitive and physically demanding world of the chimpanzeee community. The eyes still intelligent and observant and tracking everything in the environment with the attention that has been the chimpanzees characteristic from birth.
Old chimpanzees in well-established communities retain their social influence even as their physical capabilities decline. their knowledge of the range and the food resources and the social landscape of the community, having value that younger and physically stronger individuals do not yet possess.
The oldest female in a wellstudied community is often the most valuable member in terms of the ecological knowledge she carries. The knowledge of the range in all its seasonal variation.
The location of food sources that are used rarely enough that younger individuals do not know about them. The memory of what to do in conditions that have not occurred for decades and that the younger individuals have never experienced. The Gome study and Jane Goodall. We should spend more time here because the Gome study is the longest continuously running study of wild animals in the world. And what it has produced over 60 years is not just a body of scientific data, but a record of specific lives. The lives of specific individual chimpanzees followed from birth through infancy and childhood and adolescence and adulthood and old age and death. The documentation so detailed and so extended that it constitutes something genuinely unprecedented in the history of the relationship between humans and other species. Goodall named the chimpanzees, she observed, a practice that was controversial in the scientific community of the 1960s, which had not yet accepted that wild animals could be studied as individuals with specific identities. and she described their behaviors in terms that implied emotional and social complexity, terms that the scientific norms of the time considered inappropriate for the description of nonhuman animal behavior.
The resistance to her approach has faded as the findings she was reporting have been confirmed and extended by decades of subsequent research. The chimpanzees she named and observed in the 1960s were the founders of a lineage that the Gomebe study has been following for 60 years. The genealogies of the community's families documented across four generations. The social histories of individual relationships traced across decades. The record of births and deaths and alliances and conflicts. And the social changes produced by each significant event accumulated into a database that has no equivalent in the study of any other wild animal population.
Goodall's observation of the chimpanzees tool use was the finding that changed everything. When she watched the chimpanzeee, she called David Greybeard strip leaves from a twig and used it to extract termites from a termite mound and then reported the observation to Leaky in November 1960. The reverberations of that observation are still being felt 60 years later. The observation required the revision of the definition of what makes humans distinct. the revision of the boundary between the human and the non-human. The revision of the ethical framework within which we relate to the other species with whom we share the planet. If the chimpanzeee makes and uses tools, then the capacity for technology is not uniquely human. If the chimpanzeee lives in communities with cultural traditions, then culture is not uniquely human. If the chimpanzee engages in political behavior, then politics is not uniquely human. If the chimpanzee experiences something that functions like grief, then grief is not uniquely human. The list of the things that were thought to be uniquely human that the chimpanzeee has been found to share has been growing since 1960, and it continues to grow.
Each new finding requiring a new accommodation of our understanding of what the human is and what the chimpanzeee is and what the relationship between the two species actually involves. The sanctuary, the fate of orphan chimpanzees, the infants whose mothers were killed for bush meat and who were captured and sold into the illegal exotic pet trade or found starving and dying in the forest has been one of the more successful stories in the conservation of the species. The network of chimpanzeee sanctuaries established across subsahara and Africa taking in the orphaned individuals providing veterinary care and social rehabilitation and ultimately where possible reintroduction to forest in protected areas. The sanctuary rehabilitation process is long and difficult and not always successful because the orphaned infant chimpanzeee that has lost its mother has also lost its primary source of the learning that chimpanzeee development requires. the model and the teacher and the social foundation that the mother provides. And the rehabilitation process has to address not just the individual's health and physical condition, but the social and psychological disruption of early maternal loss.
The sanctuaries that are most successful are those that provide the orphaned chimpanzees with surrogate social companions and the extended social environment of a group that mimics as closely as possible the conditions under which chimpanzeee development normally occurs allowing the individuals to acquire through participation in the sanctuary community some of the behavioral skills that they would have acquired from their mothers in the wild.
The threats. The chimpanzeee faces threats from multiple directions simultaneously. The habitat loss and the hunting and the disease and the illegal trade all operating together in the specific contexts of the countries where the chimpanzeee lives. Countries that are among the poorest in the world and that face human development pressures that are both understandable and in direct conflict with the conservation of the chimpanzee and the forest it lives in. The communities that live adjacent to chimpanzeee forest depend on the forest for fuel and for farmland and for the protein that bush meat provides.
Dependencies that are not easily addressed without alternatives. And the history of conservation in these regions is littered with the failures of approaches that try to protect chimpanzees without addressing the human needs of the communities adjacent to the protected areas. The approaches that have worked to the extent that any have worked are those that have found ways to align the interests of the local communities with the preservation of the forest and the chimpanzees in it.
Creating economic stakes in the forest survival through tourism and through payments for ecosystem services and through the development of sustainable livelihood alternatives that reduce the dependence on bush meat and on forest clearance. These approaches are difficult to implement and difficult to sustain and require the ongoing commitment of resources and attention that is hard to maintain over the long term. But they are the approaches that work and they are being implemented in more places and with more success than was the case 20 years ago. The chimpanzee at play. We should return to this because play is one of the most important things the chimpanzee does and one of the most immediately engaging to the human observer who watches it and because the play of the chimpanzeee illuminates the relationship between the two species in a way that more serious behaviors do not. The juvenile chimpanzees playing in the afternoon rest period, the wrestling and the chasing and the object manipulation and the social play that involves tickling and chasing and the playface and the panting vocalization that is the chimpanzeee laugh produce an immediate and involuntary response in human observers that is recognition. The feeling of watching something familiar, something that belongs to the same register as the playing of human children, the same energy and the same social focus and the same absorption in the activity for its own sake. And the same sudden transitions from play to rest and back to play that characterize the play of any young social animal with energy to spare and social skills to develop. The play of the chimpanzeee is not trivial. It is the primary mechanism through which young chimpanzees develop the social skills that adult life in the community will require. The physical skills of the aroreal and terrestrial life they will lead. The cognitive flexibility that the variable and demanding social environment of the fish and fusion community demands. Play is practice and the quality of the play, the diversity of the play partners and the variety of the play behaviors predicts the quality of the social skills that the individual will have as an adult. The investment of the juvenile period in play being the investment in the cognitive and social capital that adult life will draw on. The chimpanzeee that plays well as a juvenile becomes the adult that navigates the community's social complexity effectively. And the adult that navigates the social complexity effectively is the individual that survives and reproduces and passes on to the next generation the behavioral dispositions that produced its success.
Play is serious. Play is the work of childhood. In the chimpanzee, as in the human, breathe now more slowly. The forest is quieter as the evening deepens. And the parties that were active through the afternoon have settled into their night trees and begun the nest building that ends each day.
The sounds of the community moving from the active vocalizations of the day to the quieter sounds of the settling group. The occasional soft call between nearby individuals. The rustling of nest construction. The quiet that descends as the last light leaves the canopy and the night begins. The chimpanzeee in its nest is not entirely the same as the chimpanzeee of the day. The highintensity social engagement of the waking hours suspended for the hours of the dark. The body at rest. The metabolic rate declining toward the minimum. The brain doing in sleep what the brain does. The consolidation of the day's experience. The maintenance and the repair that the sleeping body performs while the waking mind is quiet.
The chimpanzee in its nest is the chimpanzee at its most ancient. The nest in the tree in the forest. The same nest in the same kind of tree in the same kind of forest that the chimpanzees ancestors have been sleeping in for millions of years. The same position in the canopy above the reach of most ground level predators. The same physical arrangement of the sleeping body in the bent branch platform. The same sounds around it. The same dark.
The same breathing. The six to seven million years of separate evolutionary history that has produced the differences between the chimpanzeee and the human have not changed this have not changed the fundamental arrangement of a great ape in its forest sleeping through the dark hours in the way that great apes have always slept. The chimpanzeee in its nest is 6 to 7 million years closer to the original than you are in this specific respect. And the continuity of its sleeping posture in its sleeping place over that time is one of the most profound demonstrations of what evolutionary continuity means. The specific form of the specific behavior preserved across millions of years because the forest has not required it to change. The chimpanzees sense of humor. This claim requires careful handling because the word humor is loaded with connotations that may not apply precisely to what the chimpanzee does. But the observation that motivates the claim is real and documented.
Chimpanzees in play perform what researchers have described as practical jokes. Behaviors that appear to be directed at producing a specific response in another individual for the benefit of the joking individual.
behaviors that go beyond the normal play repertoire and that have the structure of teasing, the deliberate provocation of a response, the monitoring of the response, and the repetition of the provocation if the response is rewarding. A juvenile chimpanzee that repeatedly approaches a resting adult from behind and touches it lightly and then retreats, watching the adults startled response and repeats the behavior when the adult settles again is doing something that has the structure of teasing. Whether or not the internal experience that motivates the behavior has anything in common with the internal experience of a human being engaged in teasing, the behavior is there. What produces it is a question that requires more humility about what we can and cannot know about the inner life of another species than most discussions of this topic have shown. The chimpanzeee and death. The chimpanzees response to death, the deaths of individuals within its community has been one of the most discussed topics in the recent literature on great ape cognition and emotion. Because the observations that have been accumulated at the long-term study sites and at sanctuaries and in captive groups have been consistent enough and detailed enough to require a serious engagement with the question of what the chimpanzeee understands about death and how it responds emotionally to the deaths of individuals that matter to it. The mother carrying the dead infant is the most widely observed pattern documented at multiple sites and in multiple subspecies. The mother continuing to carry the dead infant, sometimes for days or weeks, refusing to relinquish the body, grooming it and examining it and vocalizing to it in behaviors that are clearly not adaptive that serve no function beyond whatever is expressed by the continuation of the behaviors toward the infant that were continuous when the infant was alive.
This behavior has been the subject of intense debate about its interpretation.
Does it indicate that the mother does not understand that the infant is dead?
Does it indicate that she understands but cannot act on that understanding?
Does it reflect something like denial, the emotional inability to accept the loss even when the factual state is known? The debate continues. The observations are not in dispute. At Bosu in Guinea, researchers observed the reactions of the community to the deaths of two infant chimpanzees during a respiratory virus outbreak. And what they observed was the community moving quietly through the forest, not using the loud calls that normally punctuate their ranging, staying closer together than usual, the infants being carried by their mothers in the abnormally still and quiet way that has been described in multiple accounts of chimpanzeee responses to death in the community.
at Gomebe following the death of the adult male Figan, a high-ranking individual whose social relationships had been at the center of the community's political life for years.
The behavioral changes in the surviving community members were measurable and persistent. The individuals who had been most closely allied with Figen, showing disruptions to their ranging patterns and their association patterns for months. The community knows when someone is gone. The community responds to that knowledge. The nature of the knowledge and the nature of the response are questions that we are not yet equipped to answer fully, but the behaviors that express them are real. The relationship between Goodall and the chimpanzees.
Over the decades of the Gomebe study, the relationship between Jane Goodall and the specific chimpanzees she observed evolved from the weariness of habituating wild animals to human presence through the gradual acceptance that produced the famous moment when David Greybeard allowed Goodall to sit close and then touched her hand. to the complex long-term familiarity of an observer who has been watching specific individuals for decades and who knows their individual histories and their individual personalities and their individual relationships in a way that has no parallel in the relationship between any other human and any other wild animal population. Goodall describes knowing the chimpanzees as individuals in a way that is not categorically different from the way a person knows the members of a community they have been part of for a long time.
Knowing their specific histories and their specific temperaments and the specific patterns of their specific relationships. Knowing what to expect of each individual in each situation and being surprised when they deviate from those expectations. The knowledge of specific persons that is the basis of all long-term human social relationships applied in the context of a relationship that crosses the species boundary. The crossing of the species boundary is the thing that makes the Gome study and the work of Goodall and her colleagues and successors more than a scientific enterprise though it is that it is a relationship in some meaningful sense between the human observers and the chimpanzeee community. They have been living alongside for 60 years. A relationship that is not equal and not without its ethical complications and not without the distance that is necessary for the science to remain science rather than becoming something else. But it is a relationship in which specific individuals have been known to specific other individuals for decades.
in which the births and the deaths and the social changes of the chimpanzeee community have been witnessed and recorded and reflected on by the human observers in a way that is not fully captured by the word observation in which the human knowledge of the chimpanzeee lives and the chimpanzeee knowledge of the human presence have accumulated together over time into something that does not have a precise name but that has produced in both directions a kind of familiarity the chimpanzee range at night. While the community sleeps, the territory continues to be the territory. The boundaries of the range that the adult males patrol and defend maintained by their history of use and their occasional aggressive encounters with neighboring communities. The forest full of the signs of the community's passage and the signs of neighboring communities passage. The chemical traces and the food remains and the nests that record recent presence. The forest that is the community's shared knowledge and shared resource continuing to be what it is through the sleeping hours. The leopard that is the chimpanzees primary predator is active at night moving through the forest in the silence of a solitary nocturnal predator and the chimpanzees in their high nests are largely protected from it by their elevation.
the leopard capable of climbing trees but less likely to do so for the reward of a sleeping chimpanzee in a high and unstable nest. The chimpanzees choice of sleeping tree reflects this threat. The selection of the tallest available trees, the preference for nesting high in those trees, the avoidance of ground sleeping that the gorilla practices with more equinimity because the gorilla's size makes it much less vulnerable to leopard predation. The sounds of the chimpanzeee forest at night, not silence. The forest at night is a different acoustic landscape from the forest during the day. The dal birds replaced by the nocturnal insects and frogs, and the occasional calls of night jars and owls, the continuous highfrequency background of the night insects overlaid with the specific calls of specific species that identify themselves by their calls in the dark.
The chimpanzees in their nests sometimes call in the night soft vocalizations that are different from the day's communication more like the muttering of sleeping humans than like the purposeful communication of waking individuals. And researchers who have slept near chimpanzeee sleeping trees report hearing these night sounds. The soft calls and the movements of the sleeping animals in their nests high above. The sounds of a community at rest in the place it has made for itself in the forest. The forest and the future, the Congo basin forest and the forests of West Africa that the chimpanzeee inhabits are being reduced and fragmented by the same forces that are reducing and fragmenting tropical forests everywhere. the expanding agricultural frontier and the commercial logging and the population growth and the development of infrastructure that brings roads into previously inaccessible forest and opens that forest to the settlement and the clearance that follows roads in the developing world. The projections for the chimpanzees forest habitat over the coming decades are not uniformly encouraging. The areas under formal protection are in many cases adequately protected. the national parks and reserves where the long-term study sites are located maintaining the forest within their boundaries through the conservation infrastructure that the scientific and conservation interest in the chimpanzeee has helped to build the unprotected areas, the corridor forests between the protected areas, the forest patches that are not covered by formal protection but that are essential for the connectivity between populations that the long-term genetic health of those populations requires are under more pressure and receive less protection.
The hope it exists. It is not guaranteed and it is not easily achieved, but it exists. The same hope that exists for every endangered species that has not yet been reduced beyond recovery. The hope that the decisions that will determine the future have not yet all been made, that the trajectory can be altered by action that is taken now and sustained over the coming years and decades. The chimpanzees future depends on the protection of the forest, on the management of the bushmeat trade, on the development of the conservation approaches that align human community interests with the preservation of the forest and its species, on the continuation of the research that produces the knowledge that informs the conservation. on the global awareness of what the chimpanzeee is and why it matters that produces the political and financial support for the conservation effort. All of these things are happening imperfectly and insufficiently but genuinely and the number of chimpanzees alive in the next 100 years will be determined in part by how effectively they continue to happen and expand.
The night is very deep now. The chimpanzeee community is asleep in the trees above the forest floor. The individuals in their high nests distributed through the sleeping trees that the community has used for years.
Each one built fresh tonight. Each one good enough for this night. Each one the last act of a day that has been full of the complexity and the richness of chimpanzeee life. the politics and the play and the grooming and the feeding and the vocalizations and the hundred specific interactions with specific individuals that constitute a day in the life of a chimpanzeee in the community it has grown up in and that it knows as completely as any animal knows any place. The sleeping community is connected to the sleeping forest. The same dark holding both. The same night that has been holding both for the millions of years that both have been here. The chimpanzeee in its nest is the product of 6 to 7 million years of evolution in the forest, shaped by the forest in every detail of its body and its behavior and its cognition. And the forest is the product of the millions of years of rainfall and sunlight and the ecological processes that include the chimpanzees that have been ranging through it and eating its fruit and dispersing its seeds and shaping its composition in ways both visible and invisible since long before there were humans to observe them. Let your body settle now into the same quality of rest that the sleeping chimpanzeee has in its nest. The deep rest of a body that has been fully active through the day and that is now fully at rest in the dark.
The metabolic rate at its minimum. The brain doing its maintenance work. The muscles released from the day's demands.
The chimpanzees 98.7% of shared DNA means that the cellular processes of your sleep and the cellular processes of the chimpanzees sleep are almost identical. the same neurotransmitters, the same hormonal regulation of the sleep cycle, the same stages of sleep serving the same restorative functions in both bodies.
The rest that the chimpanzeee is taking in its nest is the same rest at the cellular and the neurological level that you are beginning now. The same ancient primate rest in the dark at the end of the day preparing for the morning. The same morning will come for both. For the chimpanzeee, it will bring the pant hoots of the community waking and the descent from the sleeping trees and the formation of the day's first parties and the movement toward the food and the resumption of the social life of the community. The day that the day before prepared for and that the day after will require for you. It will bring whatever your morning brings. the specific demands of your specific life in the world that is yours. The world that is substantially different from the chimpanzees world and that rests on the 6 to 7 million years of separate evolutionary history that separates the two lineages.
But right now at this moment in the dark in the rest in the deep hours between the sleeping and the waking the distance between the two is smaller than it usually seems. The same biology is performing the same functions in both bodies. The same ancient night is holding both. The same primate rest inherited from the same primate ancestor is what both of you are doing in the dark. Sleep now. The chimpanzee is in the forest. The forest is old and wide and dark. The community is sleeping in its trees. The night holds everything.
The morning will come sleep. The pant hoot will come with the light. The first call of the first individual waking and announcing itself to the forest. The cascade of responses from the other community members updating their awareness of who is where. The day beginning in the way that it always begins with the voices of the community filling the forest with the specific acoustic signature of this community and this morning and this specific moment in the long history of a species that has been waking in the same forest and making the same sounds for millions of years. But that is morning. That is later. That is the next thing. And the next thing does not require your attention now. Sleep. The chimpanzeee is in the forest. The forest is there. The dark is there. And you are asleep in the same ancient rest that the same ancient biology provides. At the end of the day that came before the morning that will come after sleep, the chimpanzee and music. This claim also requires careful handling. The chimpanzeee does not make music in the human sense, does not compose or perform or listen to music in the way that humans do. But the chimpanzeee does produce rhythmic vocalizations and rhythmic physical behaviors that have structural features in common with music. features that are interesting to examine, not because they demonstrate that the chimpanzee is musical in the human sense, but because they illuminate the deep evolutionary roots of the behaviors that became music in the human lineage.
The pant hoot has rhythm.
The drumming on the buttress roots has rhythm. The rain dance, a behavior documented at multiple chimpanzeee study sites in which individual chimpanzees perform extended rhythmic displays in the rain or at the edge of waterfalls, swaying and stamping and producing vocalizations in patterns that have the quality of performance has been described by Goodall and other observers as one of the most enigmatic behaviors in the chimpanzees repertoire. a behavior that seems to go beyond the functional communication of the normal display and to approach something like expression for its own sake, the performance of a complex rhythmic behavior in a context that does not obviously serve the purposes of threat or intimidation or sexual display. The waterfall display at Gomebe and at other sites with permanent waterfalls.
Chimpanzees sometimes perform extended displays at the waterfall, swaying and calling and moving through the spray in behaviors that are not obviously adaptive that do not appear to serve any social communication function that appear to be directed at the waterfall itself. Goodall wrote about these displays with a characteristic restraint and a characteristic openness to the observation itself. Noting that if the chimpanzeee could talk, it might describe what it is doing in terms that humans would recognize as spiritual or aesthetic, that the display at the waterfall has the quality of a response to something overwhelming and incomprehensible. The chimpanzees response to the power of the falling water being somehow analogous to the human response to the overwhelming forces of nature that different human cultures have addressed through ritual and through art and through the various forms of the spiritual response to the natural world. The analogy may be too much. The waterfall display may have a functional explanation that has not yet been identified. But the observation is there and the question it raises about the origins of the aesthetic and the spiritual in primate biology is a genuine and interesting question that the chimpanzee in its display at the waterfall poses to the human observer in the clearest and most direct way. The chimpanzee and the human evolutionary story. We share an ancestor 6 to 7 million years ago. That ancestor was living in the forests of Africa, moving through the trees and on the ground, eating fruit and leaves and insects and whatever else the forest provided, living in a social group with the cognitive and social complexity that the great ape lineage had been developing over the millions of years before the split. From that ancestor, two lineages diverged. One lineage moved into more open environments, began to walk upright on two legs, developed a larger brain, developed language, developed technology, left Africa, spread across the globe, modified every ecosystem it entered, and eventually modified the global climate and the global chemistry. The other lineage stayed in the forest, continued to move on four limbs in the forest the way the ancestor had moved, continued to live in fish and fusion communities in the forest, continued to eat fruit and leaves, and to use simple tools, and to have a social and political life of considerable complexity, and is still there in the forests of Africa, doing what it has done since the split, having changed less in the intervening 6 to 7 million years than the other lineage has changed. This is the thing about the chimpanzeee that is most difficult to hold in the mind at once. The chimpanzeee and the human are from the same stock. The differences between them. The differences in body and brain and behavior and cognition and language and technology and social organization are the products of 6 to 7 million years of divergent evolution which is a long time in one sense and a short time in another. In the context of the Earth's history, 6 to 7 million years is a brief period, a small fraction of the time that life has been on the planet. In the context of what the two lineages have become in that time, the differences are vast. But the similarities are vaster still. And what the similarities represent is the shared biological foundation that makes both lineages what they are. the cellular and molecular and neural architecture that was present in the common ancestor and that both lineages have preserved how with modification through the millions of years of their separate histories. The chimpanzeee is not a primitive human. It is not an evolutionary stage on the way to becoming human. It is a species that has been evolving for as long as the human lineage has been evolving that has developed its own suite of adaptations to its own specific environment. And that represents a different solution to the same basic biological problems that both lineages inherited from the common ancestor. The chimpanzees solution is the forest. The human solution is the world. Both solutions work in their respective contexts. And both solutions are the products of the same amount of evolutionary time applied in different directions. The forest at the deepest hour. The forest at 4 in the morning is the forest at its most still, the nocturnal insects at their minimum, and the dawn chorus not yet begun, and the predators of the night having reached the end of their active period, and the dal animals not yet stirring, and the chimpanzees in their nests in the highest trees still asleep, the breathing of the community, the only mamalian sound in the forest, and the forest itself breathing in the sense that a forest breathes. The trees transpiring through their leaves even in the dark. The water cycling through the forest ecosystem in its continuous movement from soil to root to trunk to leaf to atmosphere to cloud to rain to soil again. The carbon cycling through the same system in a different direction. The oxygen that the forest produces as the byproduct of photosynthesis accumulating in the night air around the sleeping chimpanzees. The air that both the chimpanzee and you are breathing tonight. the air that the forest makes. The last grooming. There is always in the late afternoon as the community moves toward its sleeping trees a last round of grooming. The social maintenance behaviors that close the day the way they have been punctuating it throughout. The pairs settling into their positions and the familiar touch of the grooming fingers moving through the familiar fur. The social bond being renewed in the last light before the night takes over. The grooming that ends the day is different in quality from the grooming of the midday rest. More settled, less interrupted. The body's reduced energy at the end of the day, making the physical contact and the slow movement of the grooming more deeply comfortable and more fully relaxing. The grooming pair settling into a stillness that is already anticipating the sleep that is coming. The social touch becoming the comfort of the presence of a known body in the approaching dark.
The morning that will come in some number of hours the light will return to the forest and the first individual in the community will wake and call and the others will begin to wake and the day's first parties will form and the movement toward food will begin and the day will be what days in the chimpanzeee community always are full of the specific social interactions and the specific ecological decisions and the specific vocalizations and the specific encounters with specific ific individuals that make up the specific irreducible texture of a day in a chimpanzeee community. Different from every other day and the same as every other day in the same way that all days are both unique and continuous with the days before and after them. The morning will come. It always comes. The chimpanzeee knows this in the sense that an animal that has lived through many mornings in the same forest knows that the morning follows the night not as an abstract proposition but as the lived reality of a life that has been organized around the alternation of day and night for its entire duration. And you know it too. You will wake in the morning as you have always woken into the specific reality of your specific life. the demands and the relationships and the specific texture of a day in your community, which is larger and more complex and less immediate than the chimpanzees community in its forest. But that is still at its foundation the same thing. A network of specific relationships with specific individuals maintained over time through the accumulated interactions of daily social life. Through the currency of attention and care and the various forms of the primate social behaviors that both lineages inherited from the same common ancestor and that both lineages have been practicing in their different forms and with their different elaborations for the 6 to 7 million years since the split sleep now you are already there almost the thoughts have thinned to the point where they are barely distinguishable from the quiet of the pre-leep state. The mind at the threshold between the waking and the dreaming. The body fully settled, the breathing at its minimum. The chimpanzeee is in its nest in the forest in Africa. The forest is dark and still and full of the living systems that have been operating in it since long before any human was there to observe them. The community is asleep. The specific individuals with their specific relationships and their specific histories are suspended for the night.
The social complexity of their waking lives reduced to the simple biological fact of sleeping bodies in sleeping trees in a sleeping forest. The forest holds them. The night holds everything.
You are asleep in the ancient rest that the primate body has been taking at the end of every day since before there were humans to take it. The rest that the chimpanzee is also taking in its nest above the dark forest floor. The rest that the common ancestor took in its nest before the split. The rest that the biology requires and provides and that the night makes possible. Sleep. The chimpanzeee is in the forest. The forest is there. The morning will come. Sleep.
The pant hoot will greet the light, but not yet. Sleep. The chimpanzees hands again. We should return to the hands because the hands are the place where the biological similarity between the chimpanzee and the human is most immediately visible, most physically present, most impossible to look at without feeling the kinship that the DNA confirms.
The hand of an adult chimpanzee held open, the palm facing upward is a human hand with different proportions, wider in the palm relative to the finger length, the thumb shorter and less opposable than the human thumb. The lines of the skin and the patterns of the fingerprints unique to the individual as they are unique in every human. The nails flat and not clawed.
The texture of the skin at the fingertips thick and calloused from the daily use of the hands in the work of the chimpanzeee's life. When Jane Goodall describes the moment when David Greybeard allowed her to hold his hand in the forest at Gomebe when he closed his fingers around hers in a gesture that she interpreted as reassurance. The extraordinary quality of the moment, she describes, is partly the biological reality of the contact. The hands of two species separated by six to 7 million years of evolution making contact across that distance. The shared primate architecture of the hands recognizing itself in the touch. The chimpanzees cognitive map. The chimpanzees knowledge of its territory is stored in a cognitive map, a spatial representation of the territory that contains the locations of specific resources, the positions of specific landmarks, the roots between specific locations, and the temporal information about which resources are available at which locations in which seasons. The evidence for the chimpanzees cognitive map comes from the efficiency of its foraging. the directed routes towards specific trees that have been previously visited and found to be fruing. The anticipatory movements toward locations where the chimpanzeee expects to find food based on its knowledge of the phenology of the specific trees in its territory. A chimpanzeee moving through its forest toward a specific fruing tree it has not visited in days is using a cognitive map. the stored spatial representation of the territory guiding the movement toward the target without the need to encounter the tree directly to know where it is. The cognitive map is not static. It is updated continuously as the chimpanzeee ranges through its territory and encounters new information. The fruitting state of specific trees, the presence of other community members, the signs of neighboring communities, the condition of specific paths, and the accessibility of specific food sources.
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