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.

Introducing: The Great Apes

This Great Apes Series is presented as a platform for introducing and discussing what we scientifically know about the four “great apes” pictured below: Gorillas, Orangutans, Bonobos, and Chimpanzees, and Humans (not pictured, but use your imagination).

Left to Right: naturepl.com/T.J. Rich / WWF; David Lawson / WWF-UK; Russell A. Mittermeier / WWF; Martin Harvey / WWF

Apes are a branch of large, tailless primates which inhabit regions across the African and Asian continents. They reside in a variety of diverse environments, ranging from the  the dense rain forests of the Congo Basin chimpanzees, to the high montane forests of the Albertine Rift mountain gorillas.

The apes are categorically divided into two groups:

The Great Apes

Chimpanzees, Bonobos, Gorillas, Orangutans, and Humans

The Lesser Apes

Gibbons and Siamangs

Tree of Humans and Apes

Humans are members of the great ape family which, of course, indicates that we ourselves are primates. Contrary to beliefs that humans are the “superior” species placed high above the animal kingdom, we are only separated from our primate relatives by a few million years (pictured right).

The physical and behavioral similarities between humans and our fellow apes are not surprising, as we are closely linked by our genetic codes. Chimpanzees are  humanity’s closest living relatives, sharing an impressive 98% similarity in genetic makeup. Some might think of chimpanzees as crudely hunched,  barbaric beasts, but upon a closer look, one would begin to notice the incredible likeness in our rounded facial features, our long, grasping fingers, and our similar emotional capacity for joy, sadness, and anger. We are all deeply intertwined within a vast primate lineage stretching back 65 million years of incredible evolutionary feats and downfalls.

Apes or Monkeys?

The three primate groups: Apes, Monkeys & Prosimians

Apes are not monkeys. Despite the popular notion that all primates can be called “monkeys,” — think Curious George, who’s referred to as a monkey but is in fact a chimp! — there are actually three separate groups within the primate order: apes, monkeys, and prosimians. The apes represent a distinct line of primates which diverged from the  the monkeys and prosimians (lemurs, tarsiers, and galagos) lineage millions of years ago. Each primate species has evolved along a distinct evolutionary lineage and are characterized by unique adaptive morphology and behaviors.

In terms of differences, compared to the monkeys, apes are considerably larger, do not have tails, spend more time sitting upright, and rely on visual cues from their eyes rather than olfactory (smelling) cues from their noses. Apes also tend to produce fewer young, have longer infancy and juvenile periods, and experience overall longer lifespans.

Apes also have prehensile hands that are capable of grasping, holding, and manipulating objects, much like humans. Though unlike humans, apes tend to walk on all fours using their knuckles or hands for support.

Perhaps the most distinguishing factor separating the monkeys from the apes is that apes are considerably more intelligent. Apes have larger, more developed brains, which enable their ability to solve complex problems, learn, and communicate in a more sophisticated manner than monkeys.

In Scientific Terms…

Modern Classifications

The great apes are comprised of four primate “genera.” The picture on the right describes the hierarchy of biological classifications used to categorize all known species on earth. For example, a chimpanzee is scientifically classified as:

• Kingdom: Animalia
• Phylum: Chordata
• Class: Mammalia
• Order: Primates
• Suborder: Haplorhini
• Superfmaily: Hominoidea
• Family: Hominidae
• Genus: Pan
• Species: Troglodytes

To make things simpler, scientists refer to chimpanzees as Pan troglodytes or simply by their common name, chimpanzee or chimp.

The taxonomic family of Hominidae includes four genera of extant (currently living) primates:

• Pongo — the Bornean and Sumatran orangutan
• Gorilla — the eastern and western gorilla
• Pan — the common chimpanzee and bonobo
• Homo — humans

Lesser apes?

Gibbons and Siamangs are expert tree swingers, or “brachiaters“

The gibbons and siamangs (family name Hylobatidae) are by definition apes, but are not considered a “great ape” because they are more distantly related to the Hominidae family. Molecular evidence from a 2014 study by Lucia Carbone suggests that the Hylobatidae lineage diverged from the Hominidae lineage about 16.8 million years ago.

Thus Gibbons are are called “lesser apes“. However, renowned gibbon expert (and my former lecturer at UCL) Dr. Volker Sommer made a strong case for gibbons’ titles to be upgraded from “lesser” to “smaller apes” so as not to “belittle” their reputations.

Threats to the great apes

Despite their intelligence, resourcefulness, and strong social bonds, the apes are terribly vulnerable due to the very nature of their lives. Apes live in very small groups or even in solitude, they reproduce infrequently and only rear a few offspring in their lifetimes, and they develop slowly and reach sexual reproductive age late in life. None of these life history traits signify a sense of resilience to any threats put in their paths.

The apes — both lesser and great —  are in perilous danger of losing their habitats due to human activity in the ways of agriculture, mining, and commercial logging, which destroy natural environments and displace (or terminate) incredible numbers of species every day. Other threats that face the great apes include:

Civil War:

Many of the African great ape territories cross over with regions in the midst of civil wars which further destroys ape habitats. A recent 2016 article by Rachel Nuwer reported on the lasting damage which civil war in the Democratic Republic of Congo inflicted upon local bonobo populations. Nuwer reports that Japanese primatologists were forced to leave their study site in the Congo in the midst of its violent war, but upon their return only six years later, “They found that three of the six groups of bonobos in the northern section of the reserve had disappeared entirely. Numbers had dropped from 250 in 1991 to around 100 in 2004. Only the main study group seemed to be in fair shape compared to pre-war times.”

Poaching:

Hunting for bush meat has increased from subsistence to commercial levels, creating a greater threat to ape populations now more than ever before. Moreover, poaching has increased with the growing market of the illegal pet trade. Every day primate infants are kidnapped from their mothers (who are often killed in the process) in order to be sold to urban elites as pets or to circuses as forms of “entertainment.” According to the Great Apes Survival Partnership (GRASP) in a 2013 report, “A minimum of 22,218 great apes were lost from the wild through illegal activity from 2005 to 2011, and clear links exist with other forms of organized crime.”

Disease

The apes are also susceptible to many zoonotic diseases (transmittable disease between animals and humans). The Ebola virus, a highly infectious and often fatal disease, has been the most recent epidemic to decimate primate populations. According to GRASP’s report, in outbreak of Ebola in 1995 destroyed more than 90% of the gorilla population in norther eastern Gabon alone.

Apes and Us

The only great ape that is by no means endangered, is humanity. And we are, ironically, the primary cause of  our closest genetic relatives’ critically endangered statuses. Through perpetuating the destruction of the delicate environmental niches in which the great apes live, humanity ensures their extinction. But while humans may be single-handedly destroying our environment in the sixth mass extinction in earth’s history, there are many who still work to reestablish our relationship with the earth and the animals we share it with.

We as humans undoubtedly see facets of ourselves in our not so distant relatives, both the good and the bad. Much like ourselves, apes express their incredible intellect, their playfulness and personality, and their ability to build complex relationships with other individuals. But upon observing the aggressive temperament of a silver back gorilla or the warlike activities from a group of militant chimpanzees, humans might be forced to recognize our shared character faults. Despite the estrangement from our long lost cousins, it seems we are not such dissimilar creatures. It is important to remember this connection and reach out to the apes and other members of our large primate family before it is too late.

Gorillas, like humans, show a broad range of character complexity.

Stay tuned for the series!

My first series on the great apes (hopefully the first of many series to come!) presents a brief yet detailed overview of the fascinating primate species that have piqued scientific curiosity for centuries. Unfortunately the apes are endangered. It is most important now to learn as much as we can about them and from them in order to ensure their survival.
Each article from the series aims to inform the reader about ape morphology, evolutionary history, behavior, and conservation status, as well as fascinating discoveries from recent research publications. Words or phrases italicized in blue highlight scientific terms for you to learn as you read the series. “Recent Research” sections will be presented in green to highlight particularly interesting recent works in scientific research.

Note that unless specifically cited, all images used in this series are taken  from the free and legal platform Pixabay.com.

About the author:

I have always loved animals. Moreover, I have always loved learning about animals. Growing up in the California Bay Area, trips to the San Francisco Zoo and the California Academy of Sciences were very special moments in my childhood where I was able to witness how incredible the animals of the earth truly are.

Much like many other nature lovers, I grew up listening to the soothing voice of Sir David Attenborough commentating over the lives of wild and exotic species. I was taken by the documentary shots of shocking predatory attacks, feats of survival against the elements, and highly amusing mating rituals. Nature was a wonder and a curiosity to me, and from a young age I set my sights on learning everything I could about it.

Fast forwarding to college, I experienced any number of existential crises that most undergrads undergo in the pursuit of choosing a major and facing the inevitable what-do-I-want-to-do-with-my-life trope. Eventually I leaned towards a major in anthropology. While Anthropology, Latin for the study of humanity, is by definition a human centered field, I was drawn to it for its subfield of biological anthropology. This more scientific branch of anthropology examines the evolution of the primate lineage as it ascended towards humans (Homo sapiens) in addition to the extant (living) primates we know today.

After completing undergrad with a dissertation on vervet monkey ranging patterns under my belt, I moved on to graduate school in the UK. My MSc (master of science) program focused on human evolution and primate behavior (or “behaviour,” as I became accustomed to across the pond). Being taught by the some of the top primatologists (academics who study primate behavior) in the world was an invaluable experience — especially a trip to the London Zoo where our lecturer gave an excellent tour of the primate exhibits and provided live commentary on the behaviors we saw. I finished the program, happily exhausted, with a dissertation on the statistical analysis of the evolution of primate brain size.

Fast forwarding again to the present, I am back in the Bay Area and currently pursuing a career in wildlife behavior and conservation. In the midst of the post-grad-job-application-waiting-game, I decided to begin this blog as a way for myself to keep up with current animal behavioral research and to hone my writing skills. I also chose to begin this blog with the intention of providing education and outreach for those who are interested in animal behavior and conservation efforts in order to help preserve the beautiful and fascinating animals we share this planet with.