Chimpanzee

The chimpanzee (Pan troglodytes), or robust chimpanzee, is a species of great ape. The common chimpanzee is often called the chimpanzee (or "chimp"), but this can refer to both species in the genus Pan: the common chimpanzee and the closely related bonobo.

Pan troglodytes[1] Temporal range: 4–0 mya[2]
P. t. schweinfurthii in Kibale National Park, Uganda
Conservation status
Endangered  (IUCN 3.1)[3]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Primates
Suborder:	Haplorhini
Infraorder:	Simiiformes
Family:	Hominidae
Subfamily:	Homininae
Tribe:	Hominini
Genus:	Pan
Species:	P. troglodytes
Binomial name
Pan troglodytes (Blumenbach, 1775)
Subspecies
Pan troglodytes verus Pan troglodytes ellioti Pan troglodytes troglodytes Pan troglodytes schweinfurthii
Distribution of subspecies Pan troglodytes verus (green) P. t. ellioti (grey) P. t. troglodytes (red) P. t. schweinfurthii (blue)
Synonyms
Simia troglodytes Blumenbach, 1775 Troglodytes troglodytes (Blumenbach, 1776) Troglodytes niger E. Geoffroy, 1812 Pan niger (E. Geoffroy, 1812) Anthropopithecus troglodytes (Sutton, 1883)

Evidence from fossils and DNA sequencing show both species of chimpanzees are the closest living relatives to modern humans.^[4]

Description

The common chimpanzee is more robust than the bonobo. Adult chimps are 150 cm (4 ft 11 in) tall on average.^[5] In the wild, adult males weigh between 40 to 70 kg (88-154 lb)^[6][7][8], while adult females weigh 27 to 50 kg (60 to 110 lbs).^[9]

Its gestation period is eight to nine months. Infants nurse for up to 5 years, then stay close to their mothers for several more years.^[10] They reach puberty between ages eight and 12.^[10]

According to the Center for Great Apes, the chimpanzee's lifetime in the wild is about 40 to 50 years, and its lifespan in captivity is about 50 to 60 years.^[10]

Social behavior

The common chimpanzee lives in groups which range from 15 to 120 members^[10], although individuals travel and forage in much smaller groups during the day. They have a complex social structure.^[11]

The species lives in a male-dominated strict hierarchy with an alpha male at the top.^[11] However, there is also a hierarchy within females in the group, with an alpha female at the top.^[11] Disputes can generally be settled without the need for violence.

Males rarely leave the community where they were born; females sometimes migrate to other communities during adolescence.^[10]

Chimp leaders use various strategies to maintain power. Describing Goodall's observations, Brittany Cohen-Brown wrote:

Take two of the alpha males observed in Gombe, Frodo and Freud, for instance. Though they were brothers, each chimp had a very different leadership style. While Freud maintained control through fostering strong alliances and grooming those he wanted to keep under his command, Frodo relied heavily on aggression and brute strength. In addition to perks like mating rights, and duties like patrolling territory and breaking up fights, an alpha male always needs to be watching for the next chimp who will try to take his place.^[11]

Tool use

Nearly all chimpanzee populations have been seen using tools, modifying sticks, rocks, grass, and leaves. They use them for getting honey, termites, ants, nuts, and water. The species has also been seen making sharpened sticks to spear Senegal bushbabies out of small holes in trees. So although it is mainly a herbivore, it does eat other animals.

Eating habits

Older male chimpanzee, Uganda

While studying chimpanzees in Tanzania's Gombe National Park, Jane Goodall discovered that chimps hunt and eat smaller primates such as Colobus monkeys. Goodall watched a hunting group isolate a monkey high in a tree, blocking all possible exits. Then one chimpanzee climbed up, captured the monkey and killed it.^[12] The others then each took parts of the carcass, sharing with other members of the troop in response to begging behaviours.^[12]

The chimps at Gombe kill and eat as much as one-third of the Colobus population in the park each year.^[13] This was a major scientific discovery: it challenged previous ideas of chimp diet and behavior.

Goodall’s Gombe data have also led researchers to take a closer look at the role that hunting plays in chimp feeding habits. One recent Gombe study, for instance, concluded that the 45 members of one troop ate a ton of monkey meat per year. During one hunting binge, chimps killed 71 colobus monkeys in 68 days; one chimp alone killed 42 monkeys over five years. All told, chimps may kill and eat a third of the Gombe’s Colobus population each year. Researchers have also found that lower-ranking males often trade the meat for mating privileges; such trades may help prevent inbreeding by keeping a single group of males from fathering the majority of a troop’s children.^[13]

Aggression within the troop

Goodall also observed that aggression and violence happened within chimpanzee troops. She observed dominant females deliberately killing the young of other females in the troop in order to maintain their dominance,^[13] sometimes going as far as cannibalism.^[14][15]

She later said:

During the first ten years of [my] study I had believed […] that the Gombe chimpanzees were, for the most part, rather nicer than human beings. […] Then suddenly we found that chimpanzees could be brutal—that they, like us, had a darker side to their nature.^[14]

These findings revolutionized our knowledge of chimpanzee behaviour. They were further evidence of the social similarities between humans and chimpanzees.

Aggression between groups

If they can, male chimpanzees try to kill the male members of neighbouring groups. Males work together when they spot a chance to make a lightning raid on an isolated male from another group. They kill him. During the Gombe Chimpanzee War in the 1970s, a group of chimps killed seven of their neighbours one by one, until all were gone.^[16]

It can take years for this to happen but, when it does, the remaining females and the neighbouring territory are added to the now larger group. Attacks like this are carefully planned, done only when success is likely, and carried out in silence. Their behaviour is quite different from any other behaviour known in chimpanzees:

About every two weeks, males are drawn by some unknown signal to walk very quietly, single file, into a neighbouring territory to attack a vulnerable male... the overwhelming targets are other males.^[17]249[18]

The advantage for the males that win is to breed more children. Their tribe also holds a larger territory, and so has access to more food.^[19] Several authors have drawn a connection between this behaviour and the origins of human warfare.^{[17][20][21][22]}

Endangered status

The common chimpanzee is listed on the IUCN Red List as an endangered species. There are between 170,000 and 300,000 individuals. They live in the forests and savannahs of West and Central Africa. The biggest threats to the common chimpanzee are habitat destruction, poaching and disease.