The uncommon chimpanzee (revised 4/20/09)

photo by JL at SD zoo.

[Comments or questions by me (jl) are prefaced usually by (jl) or followed by (?)]

Be sure to read the links and readings by deWaal for general background.

Filmed at the San Diego Wild Animal Park, Escondido

The narrator here may be a bit overenthusiastic about bonobos as a model of human evolution.(jl)

Think about what a "model" is. Surely these chimps are no more closely related to us than the common chimps! I suppose it is possible they have changed less from the ancestral chimp than the common chimp has. But that makes them no closer to a human; just that a common chimp is further away!    Humans and all varieties of chimps had an ancestor some 5-7 mya.  The fact that we are more or less like a bonobo does not make them genetically or evolutionarily closer to us.  We may have both converged similarly or the common chimp changed more than humans or bonobos -- many possibilities exist.

The role of neoteny - (See Shea in EHE, p.104)?

 Bonobos greater similarity to us also be due to their relatively neoteny, i.e.. they are paedomorphic relative to common chimps with all that entails--including more human-like features. This might entail some more human-like behaviors, e.g. face to face intercourse that in turn may have implications for social relationships, etc.  Neoteny thus is a source of changes, variations, that natural selection may draw upon.

There has been little information on bonobos natural behavior

The usual reasons hold -- they are rare, maybe only 20,000 left at the time of the video and less than 100 in captivity.  deWaal in a recent interview said the number now in the wild may be down to 5000.

they live south of Zaire River (map) in Zaire (now Democratic Republic of Congo) A major study site is at Wamba.

They live in remote area surrounded by territory occupied traditionally by chimps and gorillas. I have read somewhere it is somewhat swampy and this may have contributed to their evolution as most apes dislike water but apparently not bonobos.  The first description of them as a distinct variety came in 1933.
Yerkes had a bonobo at his summer home in Franklin, NH.circa 1925.  He noted that it was quite different from his other chimps.

features:

Bonobos have rounder skulls, higher forehead, dark skin, slender and longer legs, reddish lips, and a more  graceful upright position than other chimps.

 (jl) how much of this is a neotenous development relative to common chimps?

 They travel for food, 15 kilos day, 80% time feeding --not different from other apes. Bonobos are omnivorous but eat vegetation primarily with some insects and small mammals.  I haven't heard any reports of systematic hunting like the common chimps sometimes engage in. See Wrangham's paper in TO.

no tool use observed as yet in their natural habitat

Unlike common chimps, bonobos do not seem to use "tools."  Perhaps, like the orangs, they just haven't had the environmental need nor a culture supporting it.  Surely in captivity some bonobos are excellent tool users. (See the Kanzi video where he cuts a rope with a sharp stone he "made.")
locomotion
Bonobos are very arboreal, yet engage in the typical chimp knuckle-walking and when necessary a more graceful bipedalism --perhaps a benefit of neoteny?

nest-building like common chimps
social/sexual (see below , deWaal links and readings)

society -"fission-fusion"

large groups of males and females
occasional breaking off of small groups for feeding
females tend to center of group

One suggestion for lesser of male bonobo aggression is that females are not as separated as in common chimp society; this may be due to feeding habits and sexual bonding.

Thus the females have greater choice over mates. Darwin's ideas on sexual selection suggest if females prefer lesser aggression and can reject mating with the more aggressive males, overall aggression levels will decline. One might expect testosterone levels to be lower in bonobo males than the more aggressive chimp males. (This is now known to be true!)


lots of grooming

strengthens friendship

females leave home group
males remain with their mothers (some Freudian-like speculation here!)
"hierarchies among --and not between-- the sexes"

 

reproduction

every 5 years

gestation about 8 months
nurse till 4; dependent till 7 years

patrilineal society

females leave their natal group
integrated into new group when a female becomes a mother
males stay with group and maintain a very close relation with mom
highly social and cognizant of rank
minimal within-group male competition as well as minimal cooperation compared with common chimps

apparently much less aggressive than chimps

"no murder" observed in bonobos

males have closer relationship with infants

This is perhaps a result of long maternal association, as well as lesser aggression?

minimal aggression

Less within-group violent aggression than common chimps

vocalizations- bonobos have a characteristic squeal
branch dragging
some punching and biting to express annoyance!

food sharing - especially among females builds strong bonds (as does sexual & grooming contacts)

sex as tension reduction, esp. in food sharing

highly sexual species
face to face intercourse - (enabled by frontally oriented genitals -a paedomorphic feature?)

lots of "female choice" exercised
"flashing"--exposing erect penis-- is common!
complex sexual communication

"hurry up" gestures, turn (body) around gestures, one-arm embrace to encourage sexual activity

sexually attractive in 3/4 of 46 day menstrual cycle

Dominant males become more interested around ovulation - (JL change in color of swelling and/or olfactory cues?)
g-g rubbing, masturbation, oral sex
prolonged estral swelling

Bonobos have much more interest in sex compared with common chimps, less compared with humans??

sexual expressions and gestures

JL - These sexual encounters are really quick; do they have orgasms comparable to humans? If they were human, the entire species would probably be in jail for these activities in public -- not to mention activities with juveniles!!

(Also lots of non-sexual communication, similar to other apes and humans)

activities

tickling and chasing are common play activities

 (jl) no wonder they "talk" about them!

food sharing
(why do they carry straw?)

***

JL comments and notes:

It is widely reported that female bonobos dominate male bonobos. While this is often true, I don't think it is true in all situations. Here is a paragraph from a recent study (note that most of these studies are in captive populations):

"For the moment the term nonexclusive female dominance (Vervaecke et al. 2000a) seems to apply best to the patterns of dominance in the 6 captive groups and has serious implications for interspecific comparisons. Nonexclusive female dominance in bonobos is different from complete female dominance in other species, such as spotted hyenas (Crocuta crocuta; Drea and Frank 2003) and lemurs (Lemur catta; Kappeler 1990; Propithecus diadema; Pochron et al. 2003; and Hapalemur griseus; Waeber and Hemelrijk 2003). However, female dominance among bonobos, even if nonexclusive, remains a striking contrast with chimpanzee society, wherein males generally dominate all females in the group (Goodall 1986). "

http://www.springerlink.com/content/w782071r75637542/fulltext.html

International Journal of Primatology
The Official Journal of the International Primatological Society
© Springer Science+Business Media, LLC 2007
10.1007/s10764-007-9186-9
Sex Differences in the Steepness of Dominance Hierarchies in Captive Bonobo Groups

Jeroen M. G. Stevens1, 2 Contact Information, Hilde Vervaecke4, Han de Vries3 and Linda van Elsacker2

or see this report from Wamba; Takeshi Furuichi (2004) International Journal of Primatology, 18,

Agonistic Interactions and Matrifocal Dominance Rank of Wild Bonobos (Pan paniscus) at Wamba

" Dominance between males and females is unclear, but females tended to have priority of access to food. The close social status between males and females may be related to the prolonged estrus of females and their close aggregation during ranging. Existence of a male''s mother in the group and her dominance status among females seemed to influence his dominance rank among males. "

Conjecture that bonobos are a good model for humans must deal with dissimilarites including bonobo promiscuous sex not openly seen in any human culture as far as I know, and the much greater degree of dependence of human moms on social support including that of the father.. In bonobo society, as in c chimps, fathers are unknown to anyone but the DNA investigators.

See the PBS Nova notes on the recent Bonobo video. --'Last great ape'