Great Apes Series: Chimpanzees

This article is part of the Great Ape Series which aims to introduce and discuss what we scientifically know about our close primate relatives. Please click the link for the Series Introduction.

The Chimpanzee, Frodo, from Jane Goodall’s study site in Gombe Stream National Park, Tanzania (National Geographic).

 

All About Chimps

Chimpanzees (Latin name Pan troglodytes) are a branch of the great apes native to the forests, woodlands, and grasslands of Equatorial Africa. Curious, intelligent, and highly social, it no great surprise that these fellow primates are human’s closest living relatives. Since the 1960s with Jane Goodall’s (1) groundbreaking research on chimpanzee communities in Gombe Stream National Park, scientists have examined our striking similarities, from intense social relationships, to tool use, and even warfare.

Primate Info Net

All Types of Chimps

There are currently four recognized subspecies of chimpanzee: the Western Chimpanzee (Pan troglodytes verus); the Nigeria-Cameroon Chimpanzee (P. t. ellioti); the Central Chimpanzee (P. t. troglodytes); and the Eastern Chimpanzee (P. t. schweinfurthii) (2). Though there are very few morphological differences between these subspecies.

Pan v. Homo

Some have argued that chimpanzees should actually be considered under the same genus as humans, “Homo” (3). Advocates for this view point out that chimps and humans share a remarkable 99.4% genetic similarity, and  are only separated by a mere 6 or 7 million years of evolution. Elevating their status to the “human branch” of the Hominidae family tree might permit greater protection for endangered chimpanzees, though resistance to inclusion is still high within the scientific community.

Behavior

Chimpanzee orphans, Republic of Congo. (Michael Nichols, National Geographic)

 

Chimpanzees are incredibly lively and social animals. They live in large communities comprising anywhere from 20 to 150 individuals (4) who forge friendships and care for one another, as well as bicker and fight, much like any human settlement. Their social structures are described as fission-fusion, whereby small groups break off from a larger group during the day to forage and then come back together at nighttime to sleep. Adult chimpanzees construct nests in trees to sleep in at night (5)

Chimpanzees develop strict social hierarchies within their communities, whereby males are dominant over females. Male dominance is frequently exhibit through displays of aggression and coercion towards subordinate females. Male chimps will generally stay in their natal groups (the group they were born into), while females tend to leave for a new community around sexual maturity (6). Because females disperse from their natal groups and males do not, male chimps are more likely to be related to one another within their communities; thus,  male-male social bonds tend to be stronger than female-female bonds.

Chimpanzees also have excellent memories and can remember friends and relatives, as well as enemies, from neighboring troops. When different communities reform after long absences, chimps will even greet each other with hugs and kisses (7).

Chimpanzee Parenting

 

A mother meticulously grooms her infant

 

Much like humans, chimpanzees generate strong mother-infant bonds, often lasting a lifetime. Chimps are incredibly vulnerable during infancy and rely entirely on their mothers to nurse, carry, groom, protect, and educate them until they reach maturity — this means that young chimpanzees spend about 10 years with their mothers! Because infants take so long to reach maturity, parental care is incredibly demanding on mothers, and so they only give birth to a few babies in their lifetimes (8).

Grooming

The most observed physical interaction in chimpanzees is grooming. Social grooming (or allogrooming) is an important practice for chimpanzees as a way to bond with other individuals within their communities. Chimps spend hours each day attending to their relationships by meticulously probing each others’ fur for insects and dirt. While this act has a hygienic function, it is a deeply-ingrained social practice that works to solidify social bonds between chimpanzees. Moreover, studies have shown that grooming also greatly reduces stress levels in individuals (9).

Locomotion

Chimpanzees forage and socialize in the trees as well as on the ground. They have long arms and fingers for moving arboreally along the branches of trees, but they also move terrestrially on the ground as quadrupedal knuckle walkers. Moreover, chimpanzees can stand and walk bipedally (standing on two legs), though just for short periods of time.

Walking upright lets chimps carry items — like this chimp here with hands and a mouth full of food

 

Diet

 

Chimpanzees are primarily frugivorous, meaning they mostly eat fruit.

 

Chimpanzees are omnivorous, though primarily eat fruit and supplement their diets with plants such as leaves, seeds, flowers, stems, pith, bark, and resin. Their diets are further supplemented with insects, eggs, honey, birds, and small mammals — including other primates (10).

The world was shocked by Jane Goodall’s discovery over 40 years ago that, much like early human hunters, chimpanzees actively form hunting groups to kill and eat small animals (11). Red colobus monkeys (Procolobus badius) are considered their primary prey.

Recent Research:

A hunting group sharing their prey 

 

 A study by David Watts and John Mitani (12) examined predatory behavior within a community of chimpanzees located at a study site in Kibale National Park, Uganda. Watts and Mitani have reported in their studies from 1995 to 2015 that from 556 observed hunts, 356 involved chimpanzees targeting red colobus monkeys. As a consequence, red colobus populations have actually declined by 89% and chimpanzees have been forced to find alternative prey. It is interesting to see the family resemblance in that humans are not the only ones to push other species towards extinction…

Cognition

Chimpanzees are highly intelligent beings with the mental capacity for problem solving (13),  using tools (14) to manipulate their environments, and have even demonstrated an ability to understand and communicate human language through sign language (11). It is debated as to whether chimpanzees, and the other great apes, possess a “theory of mind” (15), whereby an individual actively understands the existence of thought and self-awareness — in general terms, it implies that an individual demonstrates a sense of “consciousness” to the degree that humans possess.

Tool Use

Tool use (16) has been documented in all known populations of chimpanzee communities. Chimps use sticks to extract termites or ants from nests, rocks to crack open nuts, and leaves to soak up drinking water. While these implements are simple, employing them as tools to actively modify surrounding environments requires undeniable skill and forethought.

Culture

Skills such as termite fishing or using a hammer and anvil must be learned, practiced, and mastered in order to possess the necessary skills for survival. The ability to observe, mimic, and learn are undeniable evidence for intelligence. Moreover, actively passing down these skills from adult to juvenile, generation after generation, is evidence for simple culture (17).

Two young chimpanzees demonstrate termite fishing (left) and using a hammer and anvil (right) to crack nuts.

 

 Communication

Chimpanzees have demonstrated their own unique system of communication akin to language: they call out excitedly to one another over finding a particular food or as a warning against predators. They even vocally express feelings of joy and  laughter. Jane Goodall, in her groundbreaking book In the Shadow of Man describes a playful scene between two chimpanzees…

“Flo sometimes coped with the task of wrestling Flint from his playmates by playing with him herself. Then when she dragged him away by one foot, he apparently continued to regard it as a game, for he laughed as his back went bump, bump, bump over the uneven ground. I was reminded of Christopher Robin dragging Pooh Bear downstairs.” (In the Shadow of Man, p. 156).

Warfare

But as playful and loving as chimpanzees can be, they have also revealed a darker side. Chimpanzees are notoriously aggressive — males will bare their teeth, beat their hands against tree trunks, and drag tree branches along the ground while screeching for dramatic displays of aggression and intimidation (18).

A vicious attack from another documented chimpanzee war at Gombe.

 

Recent Research:

Nicholas Wade wrote an article for the New York Times on Dr. John Mitani’s research on chimpanzee aggression and warfare in Uganda’s Kibale National Park. Dr. Mitani describes the observed groups of male chimps as “frat boys” who hoot, holler, and beat up one another. But these playful antics have been observed in more organized and deliberate acts which can only be described as “warfare.” A group of a few males might form a patrol party that moves along the edge of their territory, checking for enemies. If an enemy male chimp from another community is found, it may be ferociously attacked, bitten, scratched, and torn apart until dead. Females are usually unharmed, but their babies might be eaten. According to Mitani’s 10 years of research, the chimpanzees in his study site in Ngogo are actively defending and building up their territory. The capacity for such deliberately violent attacks for the sake of gaining land is startlingly human. In his article, Wade mentions the important implications of chimpanzee warfare, “because of the possibility that both humans and chimps inherited an instinct for aggressive territoriality from their joint ancestor who lived some five million years ago.”

Conservation Efforts

Chimpanzees are currently listed as an endangered species by the IUCN who report, “Although Pan troglodytes is the most abundant and widespread of the great apes, and many populations exist in protected areas, the declines that have occurred are expected to continue, satisfying the criteria for an Endangered listing” (19). Falling chimpanzee populations are primarily caused by disease, habitat destruction, and poaching (20).

Disease:

Ebola outbreaks in recent years have been responsible for killing tens of thousands of chimpanzees as well as other great apes. It is reported that since the 1990s, a third of the world’s chimpanzee, as well as gorilla, population has been brutally wiped out by this virus (21). Conservationists are increasingly concerned for the health of the already endangered apes, and call for a more support in developing a vaccine to save the remaining population.

Habitat Destruction:

Many chimpanzee habitats have been destroyed to make room for farmland, to expand human settlements, and to harvest timber for trade. When trees are uprooted, important food sources such as figs are taken away from chimpanzees, and moreover, the empty space provides greater access for hunters and consequently less protection for chimps (22).

Poaching:

Bush meat is a coveted protein source for many rural Central and West Africa peoples, but the bush meat market has recently expanded to urban regions as a desire for exotic meat rises. Moreover, chimpanzee infants are frequently captured to be sold in the illegal pet trade. Chimp mothers are often killed in order to capture the infant (23).

Solutions?

Wildlife conservation organizations urge people to lend support in the hopes of saving endangered chimpanzees, among other species that are equally at risk within their shared environment. Here are some of the ways in which organizations such as the World Wildlife Fund and the African Wildlife Fund are helping the cause:

Visit the WWF site to learn how you can help!

 

• Managing protected national park areas in Central and West Africa.
• Advocating for stricter anti-poaching laws and better law enforcement.
• Surveying and researching chimpanzee populations.
• Advocating for sustainable practices for harvesting forest resources.

Perhaps the most important solution is to work with local African communities to provide education and sustainable alternative methods for agriculture and timber harvest. Learning to respect and protect chimpanzees and their delicate environments is a vital step towards forging the gap between these fascinating animals and ourselves. With the number of wild chimpanzees falling dangerously below healthy population levels, there is no time to waste in our conservation efforts. And perhaps by investing in the protection of our not-so-distant genetic relatives, we can discover more about ourselves in the process.