The chimpanzee (Pan troglodytes), the chimp
The chimpanzee (/tʃɪmpænˈzi/; Pan troglodytes), also known as simply the chimp, is a species of great ape native to the forests and savannahs of tropical Africa. It has four confirmed subspecies and a fifth proposed one. When its close relative the bonobo was more commonly known as the pygmy chimpanzee, this species was often called the common chimpanzee or the robust chimpanzee. The chimpanzee and the bonobo are the only species in the genus Pan. Evidence from fossils and DNA sequencing shows that Pan is a sister taxon to the human lineage and is humans' closest living relative.
Most scientists consider Pan troglodytes and Pan paniscus to be the closest living relatives of humans. Genetic evidence suggests that humans and Pan troglodytes shared a common ancestor 6 million years ago, after the branch that gave rise to modern gorillas split off.
Pan paniscus diverged from Pan troglodytes about 1,500,000 years ago, when part of the ancestral Pan troglodytes population crossed the Congo River and settled in isolation on the south bank. The range of Pan paniscus is limited to lowland rainforests, including the savannah border forests of southwest Africa, where the Democratic Republic of Congo is now located. Pan troglodytes are also rainforest dwellers, but their range is much wider and their habitat is more diverse and includes montane forests, seasonally arid forests and areas on the forest-savannah border, where their population density is very low.
Closest relatives of humans
Both species have body structures adapted to life in trees. Their arms are longer than their legs, their toes are considerably longer than those of humans and their shoulder girdle is very mobile. These and other skeletal and muscular features allow them to hang from branches, climb vines and tree trunks, and move nimbly in the tree canopy using both arms and legs.
Pan troglodytes and Pan paniscus feed mainly in trees, and at night they sleep in nests made of cut and broken branches. But these apes move mainly on the ground, and move on four limbs, relying on the bent finger joints of the hands (a mode of movement, typical also for gorillas.) Their bodies have a number of devices for such movement, e.g. the radial bone of the forelimbs at the junction with the wrist bone has a special ridge, which does not allow the wrist to bend under the weight of the body.
Pan paniscus is also called a "pygmy chimpanzee", but this is incorrect. They are indeed thinner than Pan troglodytes and their skulls are slightly different in shape, but Pan paniscus weighs no less than at least the smallest of the Pan troglodytes subspecies. Both species can stand upright on their two legs and often do so to get food or climb somewhere, but their movement on their hind legs seems rather clumsy compared to that of humans.
Pan troglodytes and Pan paniscus have a brain volume of 300-400 cc - the absolute value is quite high and so is the relative (in relation to body mass). Both species do well in the laboratory and, after intensive training (or if given ample opportunity to learn on their own), are able to communicate using symbols. In the wild, however, these monkeys communicate using a series of visual and vocal signals, but these have no symbolic meaning.
Pan troglodytes and Pan paniscus are excellent at predicting and manipulating the behaviour of other primates, either their relatives or humans studying their behaviour. Some zoologists believe this is possible because these apes understand that other primates can also have some desire and mental capacity, i.e. that Pan troglodytes have human-like thinking abilities. However, this is still a matter of debate.
Male Pan troglodytes and Pan paniscus are 10-20% heavier than females and relatively stronger; their tusks, which are their main weapons, are also significantly larger than those of females. Otherwise, males and females have similar body proportions.
From an early age, females periodically have swollen skin around the genitals. At first it is not regular and may last several weeks, but as the female matures, she has a regular menstrual cycle of about 35 days in Pan troglodytes and 40 days in Pan paniscus, and the swelling of the skin lasts between 12 and 20 days and occurs in the middle of each cycle. This indicates that the female is in heat, at which time she is very interested in males, often approaching them and initiating sexual contact. In the wild, Pan troglodytes usually give birth for the first time at around 13 years of age.
The young develop very slowly and require constant care from their mother until they are 4 years old (she may even nurse them during this time), with birth intervals of 5-6 years between births. Compared to other primates, male Pan troglodytes and Pan paniscus have very large testicles relative to their body weight and are capable of intensive mating. Males reach adult size at 16 years of age, but may reach sexual maturity earlier.
Pan troglodytes or just chimpanzee
Habitat: Tropical rainforests, deciduous forests, savannahs with habitats defined by the presence of evergreen fruit trees, from lowlands to 2000 m above sea level.
Body length: males 77-92 cm, females 70-85 cm, males in the wild weigh about 40 kg, females 30 kg (in zoos, however, males can weigh up to 90 kg, females up to 80 kg).
Appearance
The coat is black, often grey on the back after 20 years, there are short white wattles on both males and females; young have a tuft of white hair at the tail tuft, but this disappears as they grow. Males are usually bald with a triangular bald spot, while females have a wider bald spot; the skin of the hands and feet is black and the colour of the face varies from pink to brown to black; it tends to darken with age. Breeding: pregnancy 230-240 days.
Longevity: 40-45 years.
Conservation status: The species is endangered.
Nutritional peculiarities
Pan troglodytes and Pan paniscus are usually active from dawn to dusk; in the equatorial forest they are awake for 12-13 hours, and at least half of that time is spent feeding. Both species feed mainly on fruit and other fruits, but also on leaves, seeds, flowers, bark, stem cores and other plant parts. Pan troglodytes use about 20 plant species daily and about 300 per year for food. In their habitats, the availability of fruit varies greatly at different times of the year. Sometimes the monkeys have to make do with the fruits of the only plant species available in large quantities. Pan troglodytes feed on leaves throughout the year, but in greater quantities in seasons when fruits and berries are scarce. Pan paniscus appears to feed on the stems and core of plants more frequently than Pan troglodytes and there is more fruit in their habitat at all times of the year; these differences have important implications for the social structure of the populations of these species.
Pan troglodytes and Pan paniscus also eat some animal foods, such as insects (especially termites) and meat of various vertebrates; in Pan troglodytes, feeding on animal foods may occupy up to 5% of their feeding time. Pan troglodytes hunt more frequently than Pan paniscus, and their prey is more diverse; they hunt monkeys, pigs, forest antelope and various small mammals. Pan troglodytes tend to hunt in groups, more often males than females. Pan paniscus feed mainly on small forest antelopes and usually hunt individually, not in groups.
Nutrition
This is predominantly an individual process, but in Pan troglodytes it is not related to the process of eating meat. Sometimes males fight over prey immediately after the hunt is over, and higher-ranking males may take food from lower-ranking monkeys. However, begging for food and sharing it among community members is also quite common. Pan troglodytes that possess prey may passively allow other monkeys to take the food (share it with them), or they may actively distribute pieces of meat themselves. In Pan troglodytes, prey is usually owned by males, and they share it mainly with other males, especially their allies and grooming partners.
Social relationships
Pan troglodytes and Pan paniscus communities are inconsistent in their composition (merging and dissociating). All individuals are part of an alliance of 15-20 animals with some form of social bond between them, although there is unconfirmed evidence that some females may be members of two neighbouring communities at the same time. Members of an association treat each other more or less amicably, but relationships between associations are mostly hostile, and in Pan troglodytes more so than in Pan paniscus. Individuals belonging to the same community move and forage often, joining together in smaller groups whose size and composition may vary, all members of the community rarely (if ever) meeting together.
Group size depends largely on the availability of food, especially fruit. When fruit is abundant, the number of monkeys in groups increases and they tend to gather in large fruit trees, such as giant fig trees, but when fruit is scarce, group size decreases, presumably to reduce the stress of food competition. Average group size is slightly larger in Pan paniscus (6-15 animals) than in Pan troglodytes (3-10), with Pan paniscus having less variation in group size because the food supply in its habitat is subject to less variation.
In Pan troglodytes, males are more social than females, who, together with their cubs, are often kept apart from the group. However, in Pan paniscus, the difference in sociality between the sexes is not as pronounced. Male Pan troglodytes tend to move around more than females and use almost the entire area of their group. Females with dependent young limit their activity mainly to restricted areas in the centre of this territory, although sex differences in territory use depend on habitat.
Male Pan troglodytes and Pan paniscus remain in their home communities throughout their lives, while females often move to neighbouring communities before breeding. Adult females also sometimes change communities, but this is relatively rare.
Upon entering a new community and attempting to establish herself in the new territory, the female often encounters aggression from resident females, at which point she is dependent on the males, as only they can protect her from this violence.
The aggressiveness of resident Pan paniscus females is not as strong as in Pan troglodytes, so newly arrived females often try to establish social relationships with some of them, which will help them to gain the tolerance of other members of the group later on.
There are significant differences between the social relationships of Pan troglodytes and Pan paniscus. The Pan troglodytes community is based on social relationships between males, which are based on the principle of dominance-subordination and lead to the establishment of hierarchical relationships, although in multi-male communities this may not be as evident. Competition for dominance can be intense.
However, friendly relationships do exist between males. Males are more likely to groom and groom each other than females, and females are more likely to groom each other. Reconciliation after conflicts is also more common among males than females. Some males form alliances against other males, very important in the struggle for high rank, and the alpha male may owe his high position to the support of other males.
Females, on the other hand, do not form strong bonds with each other or with males. Some females may dominate others, but they do not form hierarchical relationships. All Pan troglodytes males dominate all females.
Facial mimicry is better developed in great apes than in any other animal. The facial mimicry of Pan troglodytes is particularly sophisticated and complex, and is used to convey a wide variety of social signals.
Unlike Pan troglodytes, Pan paniscus females group together and form strong social bonds with each other, regardless of the degree of relatedness. Sometimes females even form alliances against males and may force them to display subordinate behaviour, and at feeding times, males are more likely to cede primacy to females than to attempt to occupy feeding sites or seize food items.
Females often support their adult offspring during conflicts with other males and can influence their position in the hierarchy; as for female Pan troglodytes, in nature they play no role in the males' struggle for dominance. Male Pan paniscus also regularly groom each other, and grooming is more common in male than in female pairs, but they never form alliances like male Pan troglodytes.
When groups from two neighbouring communities meet, Pan troglodytes tend to behave excitedly and often threaten or chase each other, but if one group has many more monkeys, the other may withdraw quietly. Sometimes males will patrol the boundaries of their territories or even raid their neighbours. While patrolling, they will be on the lookout for Pan troglodytes in a neighbouring area and generally behave quietly and cautiously. If their search is successful, their reactions depend mainly on the number of monkeys in the group encountered: they retreat silently or even flee if there are fewer than their neighbours, or slightly more, but attack if their numbers greatly exceed those of their rivals. Attacks can be ferocious and deadly; male Pan troglodytes have been known to kill adult and juvenile males, cubs and even non-fertile adult females.
When groups of Pan paniscus from neighbouring communities meet, they also threaten each other and may harass. However, these encounters are sometimes peaceful - which is not characteristic of Pan troglodytes - and do not end in attacks. The mating behaviour of Pan troglodytes is very complex and variable.
Females in oestrus often mate several times with many or all males in their community, often even with immature males. Mating with a large number of males complicates paternity determination and possibly gives females some security against male infanticide.
However, when oestrus is nearing completion and ovulation (which usually occurs 1-3 days before the swelling of the skin around the genitalia ceases) is more likely, high-ranking males sometimes begin to escort females and attempt to prevent them from mating with other males.
Attempts to monopolise mating involve considerable aggression, mainly directed at the females themselves. Mating success correlates with male rank, and high-ranking males are likely to have advantages and be able to impregnate more females. Pregnancy lasts about 7.5 months. Once the female becomes pregnant, she stops cycling for 4 years, or even longer, if the offspring survive.
Use of implements
Pan troglodytes use a variety of implements: broomsticks, leaf sponges, twigs used to extract bone marrow from bones, and sticks and stones used as hammer and anvil.
Both types of feeding (social insects and fruits) usually require the use of utensils, although different populations use them differently. Most social insects have strong defences (venom), which can be dealt with using sticks or soft stalks.
Pan troglodytes make smooth, sturdy sticks 60-70 cm long (long enough to reach stray ants), drop them into an open nest, wait for ants to crawl over them, and then shake the insects into their mouths before they can sting. To get the right size and shape, the monkeys bite a blade of grass and insert it into the termite mound. The termite-soldiers bite into the grass stalk and remain there long enough for the ants to pull them out and eat them. The sticks are also used to widen the holes in the logs, which are necessary to reach the termites or wood ants.
Another type of food for which eating tools are used are fruits with hard shells, which are too hard for Pan troglodytes to bite into. Sticks and stones weighing up to 1.5 kg are used to break the peel (or rind) of these fruits, which are sometimes thrown onto stone platforms that serve as anvils. Rounded depressions are often found in the centre of these platforms, indicating that the Pan troglodytes have been using them for a long time (centuries).
But the tools are not only used for feeding. Adult males throw sticks or stones weighing up to 4 kg or more during threatening demonstrations. A case has also been recorded of the use of a throwing projectile during a hunt: a male hit an adult pig from a distance of five metres and frightened it so much that it fled and allowed him to grab the piglet.
Young Pan troglodytes have to observe, learn and practice for years to master the use of certain tools, especially the hammer and the anvil. Different populations use them differently: these are the most striking differences transmitted by social learning (the so-called "cultural traditions" in Pan troglodytes). Pan troglodytes also use implements, but not as diversely and not as often.
Pan paniscus females remain in oestrus longer than Pan troglodytes. They continue to show oestrus-like behaviour even during gestation, and the skin around their genitalia swells again one year after the birth of the young. Therefore, the sexual behaviour of Pan paniscus females is less related to conception than that of Pan troglodytes, and this may explain the fact that neither attempts at female hoarding nor infanticide are observed in Pan paniscus. Sexual behaviour is observed more frequently in Pan paniscus than in Pan troglodytes and serves several social functions. Genital rubbing and copulation are common at the time of reconciliation after conflicts and during begging for food.
It is uncertain whether we will find answers to the still unresolved questions about the behaviour of Pan troglodytes and Pan paniscus, as the future is extremely uncertain for both species. Much of their range remains intact, but most is threatened by destruction due to logging, conversion of agricultural land and other forms of human intervention. Habitat destruction and hunting are particularly fearsome for Pan troglodytes and Pan paniscus, as they are characterised by very low reproductive rates and population densities. The survival of these species in the wild will depend on continued intensive conservation efforts and, above all, on solving the problems that lead to habitat destruction and incessant hunting.
Subspecies of Pan troglodytes
- The western chimpanzee or West African chimpanzee (Pan troglodytes verus).
- The central common chimpanzee (Pan troglodytes troglodytes troglodytes). Eastern chimpanzee (Pan troglodytes schweinfurthii).
- Pan troglodytes ellioti.
- Pan troglodytes marungensis.
