by Jane Goodall
Within each chimpanzee community, there is an adult-male hierarchy in which each knows his place. And almost always, one male is clearly the number one, or “alpha.” Usually, females are dominated by adult males. The dominance hierarchy of the females is less clear-cut, but some are obviously dominant and some clearly low-ranking. Although males may fight fiercely to attain the alpha position, this elevated status does not guarantee exclusive mating rights or the best food, but it does mean that all the others show deference.
Gremlin sits with twins Glitta and Golden. They are the only Gombe twins known to have survived into adulthood.
Minutes after her infant is born, this mother chimpanzee in the Republic of the Congo tenderly caresses the baby’s tiny foot.
Gremlin rests with twin daughters Golden and Glitta, while her daughter Gaia grooms her. Behind Gremlin sits her son Galahad.
CHIMPANZEE FACTS
DURING FIFTY YEARS STUDYING FREE-RANGING CHIMPANZEES AT GOMBE, JANE GOODALL, HER STUDENTS, AND FIELD STAFF HAVE OBSERVED ALL ASPECTS OF BEHAVIOR AND THE LIFE CYCLE FROM BIRTH TO DEATH.
GENERAL
• Chimpanzees show intellectual abilities once thought unique to humans.
• Like us, they experience emotions such as joy, sadness, fear, and despair.
• They can be infected with all human contagious diseases (except cholera)—and we can catch theirs.
• The structure of their DNA differs from that of humans by just over 1 percent.
• Humans and chimps can exchange blood (if the blood groups are matched).
• Unlike humans, chimps do not swim or cry tears.
FEEDING
• Chimpanzees, like humans, are omnivorous, eating meat, eggs, and insects, as well as fruits, leaves, shoots, blossoms, stems, and bark.
• They are successful hunters, sometimes showing sophisticated cooperation.
• They often eat mouthfuls of leaves with each bite of meat, as we eat vegetables.
• They rarely show cannibalistic behavior.
TOOLS
• Chimpanzees use many objects as tools, and also modify them if necessary:
grass stems or twigs stripped of leaves to extract termites from their nests
sticks to feed on army ants and investigate things they cannot or do not want to touch
leaves to wipe dirt off themselves or, crumpled as sponges, to sop up water they cannot reach with their lips
rocks and branches as weapons
SHARING
• Most sharing among chimpanzees occurs between mothers and infants. But adults will share meat after a successful kill, in response to begging.
• One adolescent female, on three occasions, climbed down from a tall tree with food in her mouth and hand to feed her old, sick mother.
COMMUNICATION
• Chimpanzees have a rich repertoire of calls, each in their own distinct voice.
• Many of their postures and gestures are uncannily like some of our own: When greeting, chimpanzees embrace, hold hands, kiss, and pat one another. This helps calm excited or nervous individuals.
• Aggression among chimpanzees includes threats (waving arms and swaggering) and attacks (punching, kicking, stamping, biting). Females sometimes scratch and pull each other’s hair.
• Disputes between chimpanzees are often solved by threats.
• Attacked victims often adopt a submissive, appeasing posture, which usually triggers reassurance—patting, embracing, or kissing—from the aggressor, restoring social harmony.
• Long sessions of social grooming serve to reinforce friendships and provide relaxation.
LIFE STAGES
• A chimpanzee’s first tooth appears at about three months. Permanent teeth start coming in during the fifth year.
• Solid food is not an important part of the chimpanzee diet until the age of three.
• Chimpanzees experience a long period of infant dependence on the mother. An infant suckles, rides the mother’s back, and sleeps in the night nest during the first five years, or until the next infant is born.
• Male puberty is reached at nine years old, and social maturity around age thirteen. Adolescence can be a frustrating time for males, who become more aggressive toward females but must be cautious with adult males, who fascinate yet frighten them.
• The female develops her first small swellings of the sex skin when she is about eight and is mated by infant and juvenile males. But she is not interesting to the mature males until she is about ten years old. In Gombe females don’t conceive until eleven or twelve.
• Wild chimpanzees begin to look old when they are about forty-five years old. Captive chimps have lived as long as sixty-five years.
SOCIETY
• Chimps live in a complex society. All fifty or so members of the community know each other as individuals.
• Theirs is a male-dominated society in which adult males compete for top rank (alpha male) and may reign for as long as ten years.
• Chimpanzees are aggressively territorial.
• Males patrol boundaries regularly and will attack “stranger” males and females, who often die of their wounds.
REPRODUCTION
• Females generally give birth to one infant at a time. Only four sets of twins are known to have been born in Gombe since Jane’s research began; three sets to the “G” family.
• There is an interval of about five years between live births. If an infant dies, the mother can become pregnant again within a couple of months.
• Pregnancy is eight lunar months.
• A sexually receptive female might be mated by males one after the other. Some males show possessive behavior and try to inhibit other males from mating, or a male will persuade or force a female to follow him on a “consort-ship,” when he keeps her to himself.
• Infant mortality is high, and a female is unlikely to raise more than three offspring to full social maturity during her lifetime.
• Excessive inbreeding is avoided because of two factors: the first being that females often transfer to another community before breeding and the second being a sexual inhibition—like an incest taboo—that typically prevents mating between mother and son and, to some extent, between brother and sister and even father and daughter.
• Some females have more sex appeal than others. Often an old and experienced female is more popular than a young and nervous female.
THE FAMILY
• The mother is responsible for raising her infants. There are good chimpanzee mothers and bad ones. Most, however, are extraordinarily patient, tolerant, affectionate, and playful.
• All males show protective behavior to infants in their own communities.
• A sister or brother will play with, groom, and help protect a new sibling.
• Bonds between family members are close, affectionate, supportive, and may last through life.
• After the death of a mother, her infant—even though nutritionally independent—may be unable to recover from the trauma and may die.
• Older siblings typically adopt their young brothers or sisters if the mother dies. Males can be very competent care-givers; however, if the orphan is under three years and dependent on mother’s milk, it will die anyway.
Communication
Relationships among adult chimpanzees are complex. Prior to Jane’s studies, it was assumed that chimpanzees lived in harems, with a single alpha male and several females. In fact, they live in social groups within which each individual knows each other; but while some spend much time together, others meet but seldom. The small, scattered groups of a community maintain contact with each other through their calls.
Frodo is bristled and tense during a conflict. A few months later he became the alpha male of the Kasekela community.
Titan pant-hoots.
Chimpanzees use a variety of sounds, each of which expresses a specific emotion and is understood by those who hear it. Calls range from the rather low-pitch
ed hoo of the worried individual, the soft pant-grunts of greeting, to the loud, excited calls and screams that occur when delicious food is found or when two groups meet. One call, given in defiance of a possible predator or during aggressive interactions, can be described as a loud wraaaah. This is a single, drawn-out syllable, several times repeated, and can be a savage and even spine-chilling sound. Another characteristic call is the pant-hoot—a series of hoots, the breath drawn in audibly after each hoot, and often ending with three or four roars. There are several variations on this theme, but its most important function is to identify the caller, for the pant-hoot of each chimpanzee is distinctive. Hearing a pant-hoot, an individual can decide whether to reply, return the vocalization, or hasten away.
Chimpanzees also communicate by touch and gesture. A mother will touch her child when she is about to move away, and may tap on a tree trunk when she wants the youngster to come down. A chimpanzee who wants food will hold out a hand—palm up—in a humanlike gesture of begging. Friends greeting each other after a separation may embrace, kiss, or pat one another on the back. Less friendly individuals may swagger and wave their fists in the air. Angry or alarmed individuals will always erect the body hair, which is the effect you would get if a slightly built human male, with a bare torso, could cram two years of bodybuilding into a second.
Males sometimes perform spectacularly at the start of a heavy rainstorm, charging rhythmically across the ground, slapping and stamping, swaying vegetation, throwing a branch. In her book In the Shadow of Man, Jane describes the first time she saw a group of males performing their “rain dance”: “At about noon the first heavy drops of rain began to fall. The chimpanzees climbed out of the tree and one after the other plodded up the steep grassy slope toward the open ridge at the top. There were seven adult males in the group, including Goliath and David Greybeard, several females, and a few youngsters. As they reached the ridge, the chimpanzees paused. At that moment the storm broke. The rain was torrential, and the sudden clap of thunder, right overhead, made me jump. As if this were a signal, one of the big males stood upright and as he swayed and swaggered rhythmically from foot to foot, I could just hear the rising crescendo of his pant-hoots above the beating of the rain. Then he charged off, flat-out down the slope toward the trees he had just left. He ran some thirty yards, and then, swinging round the trunk of a small tree to break his headlong rush, leaped into the low branches and sat motionless.
Jane pant-hoots with orphan Uruhara, who was rescued, emaciated and nearly hairless, by the Jane Goodall Institute and brought to the Sweetwaters Sanctuary.
“Almost at once two other males charged after him. One broke off a low branch from a tree as he ran and brandished it in the air before hurling it ahead of him. The other, as he reached the end of his run, stood upright and rhythmically swayed the branches of a tree back and forth before seizing a huge branch and dragging it farther down the slope. A fourth male, as he, too, charged, leaped into a tree and almost, without breaking his speed, tore off a large branch, leaped with it to the ground, and continued down the slope. As the last two males called and charged down, the one who had started the whole performance climbed from his tree and began plodding up the slope again. The others, who had also climbed into trees near the bottom of the slope, followed suit. When they reached the ridge, they started charging down all over again, one after the other, with equal vigor.
“The females and youngsters had climbed into trees near the top of the rise as soon as the displays had begun, and there they remained watching throughout the whole performance. … I could only watch and marvel at the magnificence of those splendid creatures. With a display of strength and vigor such as this, primitive man himself might have challenged the elements.”
Threatening gestures and calls are more frequent in chimpanzees than are actual physical fights. When fights do break out, the most common causes are competition for status, defense of family members, and frustration that leads a thwarted individual to vent his aggression on a smaller or weaker bystander. Fights also may break out over food or access to a female.
Territorial Aggression
A chimpanzee community has a home range within which its members roam in nomadic fashion. At Gombe, the home range of the main study community has fluctuated between five and nineteen square kilometers. The adult males, usually in groups of three or more, quite regularly patrol the boundaries, keeping close together, silent, and alert. If the patrol meets up with a similarly sized group from another community, both sides, after exchanging threats, are likely to withdraw discreetly back into home ground. But if a patrol meets a single individual or a mother and child, then the patrolling males usually chase and, if they can, attack.
Charging displays help males rise to dominance.
In the early 1970s, the main study community at Gombe began to divide. Seven males and three females with offspring established themselves in the southern (Kahama) part of the original home range. During the next two years, these individuals returned to the north less and less frequently. Eventually they completely separated from the main group.
For a time the situation seemed fairly peaceful. If groups of the northern (Kasekela) and southern communities met near their common boundary, the males would display, calling loudly, drumming on the trees, dragging branches as they charged back and forth. These displays served to persuade members of both groups to turn back into their respective home ranges.
Males patrol their territory.
Then, in early 1974, violence broke out between the two groups when five chimpanzees from the Kasekela community caught a single male of the Kahama group and brutally attacked him. He subsequently died of his wounds. The Kasekela males repeated these attacks again and again. Even Kahama females did not escape this violence. By the end of 1977, five males and one female had been killed and the remaining adults had disappeared. Only the adolescent females had escaped the violence. The victorious males tried to recruit them, but failed. The researchers at Gombe had observed a phenomenon rarely recorded in field studies: the gradual extermination of one group of primates by another, stronger group. Over the years, chimpanzees in all three communities in Gombe continued to vie for territory, with sometimes fatal consequences.
While such brutality is disturbing, Jane is quick to point out that chimpanzees are also capable of altruism. For example, two infants, Mel and Darbee, each about three and a half years old, were orphaned by a pneumonia epidemic. Both orphans were at first adopted by unrelated adolescent males, Spindle and Beethoven, who had lost their own mothers. Spindle would even share his night nest and allow Mel to ride, clinging to his belly, if it was rainy and cold. Later, both orphans were taken on by a childless female, Gigi.
Through the years, Gombe researchers have continued to look at chimpanzee feeding behavior, ecology, infant development, and aggression. They have also documented details of chimpanzee “consortships”—when males manage to lead females away to the periphery of the home range. Once there the male can relax without fear of competition for mating. Jane suggests that chimpanzees thus show a latent capacity to develop more permanent bonds similar to monogamy or, at any rate, serial monogamy.
A group of chimps gathers in a single tree to feed.
Research Today
After a half century of research, a synthesis of the life of the Gombe chimpanzees has emerged. It validates and greatly expands Jane’s early observations. For while Jane started her research with little more than a pencil, notebook, and binoculars, sophisticated new technology enables today’s researchers to collect more detailed data. These new tools include the use of laptops in the field (for quicker and more comprehensive analysis of data collected), global positioning system handsets, and geographic information system software, all of which enable accurate mapping of chimp ranges and natural resources. Satellite imagery allows measurement of habitat types and their changes over time.
In addition, noninvasive sampling of urine and dung can measure sex hormones,
stress hormones, SIVcpz (a virus almost certainly ancestral to HIV), and signs of other infections. Fecal samples can provide enough DNA to confirm paternity and other genetic relationships, allowing us to explore new questions, such as whether fathers and their biological offspring enjoy special relationships (avoiding mating or behaving as allies, for example).
New research methods allow something else as well. We can now look outward to survey the whole of Gombe National Park, documenting and better understanding how human communities and chimpanzees compete for space. The clear task at hand: Trying to achieve ecological balance.
Two forest monitors from the Greater Gombe Ecosystem and the Masito-Ugalla Ecosystem are training to use Google Android mobile phones to collect GPS observations of the status and trends of their village forests, wildlife, and threats.