Bonobo

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(CC) Photo: Matthew Bietz; Stephen Ewen
A bonobo.

The Bonobo (pan paniscus) is a part of the ''Hominidae'' family which also includes the Chimpanzee, the Gibbon, the Gorilla, the Orangutan, and the Human. This species of ape can be found in a relatively small region: the lowland rain forest along the Congo River in The Republic of the Congo. It lives in communities that range from 30 to 100 individuals that occupies areas 22 to 60 square km. Each community is broken up into parties, and these parties are made up of 12 to 15 individuals, however the membership is always in fluctuation.

What is in a Name?

The Bonobo has commonly been linked to the chimpanzee as a "Pygmy Chimpanzee" however this classification has been deteriorating in use due to the fact that the name gives false implications about the species. The pygmy portion of the name was given after a study of a Chimpanzee's bones and a Bonobo's bones. The study found the latter to be more gracile in comparison to the former's, thus the name was given. However the Bonobo is in fact an entirely seperate species from the Chimpanzee, in fact it is as closely related to them as humans are. According to Mitochondrial DNA research the Chimpanzee and Bonobo species likely split from each other about 1.5 to 2 million years ago.

Features

Body and Build

The Bonobo is a quadruped, meaning that it walks on all four limbs rather than two like us. A unique feature to this quadruped's walking is in the use of it's knuckles. Rather than walking on the palm of it's hands the Bonobo puts all of it's weight onto it's knuckles, thus termed: knuckle walking. Due to this form of walking and the extensive arboreal lifestyle it leads, the fingers and toes of the Bonobo are slightly curved. This species of ape, unlike others, has very little [sexual dimorphism]. The male weighs an average of about 39 kg and the female about 31 kg. Despite the small difference in weight, when standing erectly both sexes are about the same height. At birth the Bonobo has darker skin and entirely black fur, this remains this way until old age, in which some gray can be seen. An easy way to recognize the Bonobo from the Chimpanzee is to refer to it's hair. The hair on the top of it's head tends to flair out just above it's ears. When compared to Chimpanzees the Bonobo has less prognathism, in other words it's face is flatter. It's ears are also relatively smaller. If placed next to a Chimpanzee, it would become very apparent that the Bonobo has a slighter more gracile build. Making it's body weight about 20% less.

Skeletal Morphology

The skull shows some resemblance to that of a Chimpanzee adolescent. This lead anthropologists to further research on the Bonobo's skull. As a result, they found that it exhibits some paedomorphism or youthful traits maintained through out life. The skull does not however show any signs of [sagital crest|sagital cresting] or [nuchal crest|nuchal cresting] that is sometimes observed in Chimpanzees and almost always in Gorillas. In comparison to the Chimpanzee's skull, the Bonobo has a relatively smaller brain case meaning a smaller cranial capacity. The Bonobo's overall more gracile build can be attributed to it's skeletal make up. Bonobos, when compared to Chimpanzee's, have narrower chests, smaller [clavicle|clavicles], elongated [scapula|scapulas] and shorter forelimbs and hindlimbs.

Sociality

The average large group of Bonobos contains a relatively equal number of both males and females. If one sex were to out number the other in the group, it would be the females. Females and their young make up the core of the groups, while the male number varies depending on the size of the group and the season. In smaller group it is normal to see the majority of it populated by females with only a couple or even no males. Males will also leave the group when certain foods, depending on the season, become scarce thus leaving only the core members.

Dominance

Dominance, although not a main component to the group's social life, does play a small role. Unlike Chimpanzee societies where there is a dominant male, females in a Bonobo society can often have control, especially when food and sex are in question. Females are able to have control over food resources using a "sex-for-food" exchange. This exchange involves a female taking control over a certain food resource by with-holding or giving sex. This sex is not limited to just males, females use this technique with other females in the group as well. The sex-for-food exchange with other females functions as a tension reducing technique and creates long term, strong relationships, in which both parties are able to jointly raise their status over males. Thus creating dominant females within the society. The way the society itself is set up also allows for females to gain this dominance. In Chimpanzee societies, the males create the core of the group while females are able to come and go. Bonobos, as mentioned before are the opposite, thus lending towards the possibility of females taking the dominant role in some cases. This is not to say that males are never in the dominant position. It is important to remember however that dominance is not a huge role player in a Bonobo society. If one sex is dominant over the other, that dominant sex does not get many benefits or have the opportunity to hold that power over other members of that society.

Aggression

Bonobos are typically known to be the peaceful ape, especially when compared to it's sister species. Aggression is rarely observed in males, even when females and copulation are in question. The most a frustrated male will do is shake a tree branch, either in order to get a females attention in the situation in which sex is involved, or as a form of intimidation. If a fight does occur it contains superficial movements, such as kicking or slapping, rather than using movements typical of a Chimpanzee such as biting or the use of weapons. These fights are usually over quickly and the opponents leave with minor injuries.

The only other time a Bonobo can be seen employing a demonstration of aggression is when two communities encounter each other. There is never any physical contact; if there is any show of aggression at all one group member will rush at strangers, in which case the intruders will leave. This is sometimes not even needed because when they meet the intruding community will often voluntarily leave. It has however been observed that when a small group of females encounters a larger, mixed-sex group of strangers, the females will show significant signs of fear and run away. The intruders do not necessarily show a sign of aggression but the presence of multiple males will be enough to send the females into a panic and flee. Aggression is uncommon but the chance of an encounter with a different community is extremely likely. Community boundaries in Bonobo regions are vague and often overlap considerably. Encounters could even occur at the center of a community's home range. These encounter are usually prompted by ripening fruit trees and near a plentiful food center.

Nest Building

The Bonobo's more slender and gracile body type can likely be attributed to the niche it has become so well adapted to. With a lighter body weight, Bonobo's are able to maneuver the canopy, where the majority of the fruit grows, with little difficulty. There are drawbacks to being so far from the forest floor, there is little space to lay out and relax. To this Bonobo's have developed a specialized behavior: nest building.

There are two types of nests that can be found in the Bonobo's region, day nests and night nests. Day nests are built opportunistically throughout the day as they feed. Here they can rest and females can safely put their infants and toddlers down without the fear of them falling. Since they are meant to only last for a short amount of time, there is not a lot of effort or time placed into their making. Night nests, in comparison, are made meticulously. A Bonobo makes this nest with great care, taking the time to assure for safety and comfort. The nest, after all, does need to last an entire night.

When it comes to building the nest Bonobos prefer certain trees, they will sometimes travel out of their way in order to build a night nest. Of the 80 possible species that they could choose from only 24 types are taken advantage of, 5 of which are used the majority of the time. It has been noted by researchers that trees are chosen according to the leaf size and the build of the branches. In order for Bonobos to make a nest, the tree's branches must be strong and flexible enough to be bent over considerably without snapping in half. But they must also have a certain amount of rigidity to them on order for the branch to slightly split. It is due to this splitting that anthropologists and primatologists are able to study them. After splitting, the tree will repair itself by filling the split in with new bark. As a result trees can be seen with branches that are permanently bent over. Researchers have been able to find some nests believed to be over 50 years old. To build the nest itself, Bonobos bend larger branches in towards the center and stamp them down. The nest is then filled in with leaves and twigs for padding. Assuming that a Bonobo builds 1-2 nests everyday, a single Bonobo can build as many as 19,000 nests in it's lifetime.

Sexual Behavior

Bonobos are unique to the animal kingdom when it comes to some of their sexual practices, in fact their practices can be closely tied to those of humans. Copulation to this species acts as more than a way to reproduce, but as a way to bond and strengthen the popultion. With this purpose sex occurs for multiple reasons and on multiple occasions: greeting, great excitement over food or dominance displays or for diffusing tension. Since the purpose of sex is not done with the singular purpose of reproducing, sex is not limited to only heterosexual encounters.

Copulation is able to occur as often as it does because females will engage in sex during menstruation and pregnancy, and they become receptive again shortly after giving birth. A female enters into estrus every five weeks. During this time the skin around the genitals swells to an enormous size, thus signaling her readiness to mate. This swelling has been known to last for up to half of her cycle, therefore allowing for more copulation. While in this state intimidation and competition by males is rare, in fact 1/4 of the time the female initiates. Even with the largest amount of sex occuring of all the apes, Bonobos have no greater reproductive success.

Sexual Positions

It is the positions that Bonobos utilize for sex that is partially why their sexual behavior is so unique. Bonobos use both the ventro-dorsal (from behind) and the ventro-vetral (face-to-face) positions. In the wild, they are likely to be observed using the ventro-dorsal postion the majority of the time, but in captivity they are less likely to use ventro-dorsal. The position used however may be up to more than whether or not they are in the wild. The size of the male and the females offspring play a role in the decision process. If there is offspring, the couple is likely to use ventro-ventral so that the mother can hold the offspring or keep it close by. Personal preference may be a factor as well. Females lean towards the ventro-ventral position, while males are more inclined towards the other. Thus ventro-dorsal is used more often because males are the initiators and the dominant figure in the the relationship. However if a female is to mate with a male that is less dominant than her or younger, they will use the ventro-ventral postion.

Courtship

Courtship is usually when a male approaches a female, displaying his erect penis. If she accepts his offer, she will back up to him and stand quadrupedally or lay on her stomach, if is it done in the ventro-dorsal position. If it is performed in the ventro-ventral position the female will lay on her back and wrap her legs around the male. It has also been observed on rare occasions with the male in the inferior position.

Specific Behaviors Associated With Copulation

It is not unusual to see a pair of Bonobos engaging in sex with the female holding her infant or with the young Bonobo in close proximity to the action. The infant is not the only observer, when two Bonobos begin to mate it will generally generate a crowd of sub-adults and adults. This is not because other males are upset by the union, they are likely observing because they want to join in, as well as the observing females. A special feature to the ventro-ventral position and on occasion the ventro-dorsal position is eye contact. The male and female will maintain eye contact throughout the copulation only breaking when they themselves part ways. When done in the ventro-dorsal position the female will turn her head around in order to meet the male's eyes.

Same Gender

It is as likely to see a male and a female partaking in sex as it is to see two females together. This is call "genito-gential rubbing" or GG rubbing for short. The two females will embrace each other in a seated or laying down position and commence to rub their genitals together as done in heterosexual sex. GG rubbing begins in childhood for Bonobos, two adolescent females will rub their genitals together while playing on a regular basis. GG rubbing os most often seen during feeding sessions, which helps to strengthen the female's relationships. This female-female copulation is sometimes done to beg for food or attract the attention of a male. However it is believed that the main purpose of it, like heterosexual sex, is to help maintain a peaceful life by acting as a tension reducing mechanism.

Male-male sex does not occur nearly as often as GG rubbing is seen in females. However it does still occur, but likely for different purposes. Rather than acting as a tension reducing mechanism, males likely use sex between themselves as a way to prove their dominance over younger or less dominant males than themselves. This type of sex has been observed in both the ventro-dorsal and ventro-ventral positions. Males are also known to engage in "penis-fencing". In this case two males will stand bipedally, using surrounding tree branches as support and rub their erect penises together.

Famous Bonobos

Kanzi and his sister Panbanisha are two of the most famous Bonobos because of the experiments they have been involved in over the last two decades. They have have both been involved in extensive research in the use of language, many claiming they are close to a human level of comprehension. Kanzi is also famous for his development with tool making. See "Tool Making" in article for further information.

The Phylogeny Debate

Some researchers developed a theory about the Bonobo's skeletal make-up and it's surprising resemblance to that of the extinct Australopithecine's skeletal remains. After comparing the two, a hypothesis was created claiming that the Bonobo was the proto-form of these extinct hominid species. However many anthropologists objected to this idea. The Chimpanzee and Hominids diverged from each other about 5 million years ago, each taking separate evolutionary paths. The Bonobo did not diverge from the Chimpanzee until about 1.5 million years ago. This means that it's relation to the Chimpanzee is much closer than to the Australopithecines. One theory objecting to the Bonobo's relation to ancient hominids is that the build of the ape is actually an adaption to their unique ecological environment. This claim noted that the Bonobo's pelvis is suited for quadrupedal knuckle walking, whereas bipedalism was a defining factor in making the Australopithecines hominids. However the debate continues.