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The Brutal Ape vs. the Sexy Ape?

Craig Stanford

Held Captive to Sex?

How real are these distinctions between chimpanzees and bonobos? Captive bonobos are indeed hypersexual, far exceeding their chimpanzee kin in both the quantity and quality of their sexual couplings, but whether this accurately reflects the behavior of wild bonobos is another question. Many of the stark behavioral contrasts are based on comparisons between wild chimpanzees and captive bonobos. Most of the available bonobo data come from captive groups in the San Diego Zoo and at Yerkes. Animals in captive settings are known for their tendency to display greater frequencies of various social behaviors compared to their wild counterparts. There is often not much else to do in captivity, where animals have no need to spend their day foraging for food. Their behavior patterns do not necessarily reflect those that evolved for living in an African forest.

So we should more appropriately turn to studies of wild bonobo populations. Although much less studied than chimps, we know about naturalistic patterns of bonobos from two long-term study sites in the Democratic Republic of the Congo: Wamba, the site directed by Kano, and Lomako, which has been occupied by two separate research teams from the United States and Germany.

The field data show that in two important respects, female bonobos are not more sexual than their chimpanzee counterparts. First, there is no difference in frequency of copulations when wild bonobos from Wamba are compared with wild chimps at either Tanzanian site, Gombe or Mahale. Second, the idea that bonobo females are released from estrus results from data on the duration of sexual swelling taken mainly from animals at Yerkes, where they maintain their sexual swelling for 23 days, nearly half of their 49-day cycle (in captivity). This dwarfs the receptive period of wild female chimpanzees from Gombe, who swell for about 13 days of their 36-day cycle. The equation changes if we consider wild bonobos rather than captive specimens, whose excellent nutrition may produce earlier menarche and ratcheted-up reproductive cycling. Bonobos from Wamba in the Congo are swollen for only 13 days of a 33-day cycle, numbers that are much closer to those of wild chimpanzees. A recent report about bonobos in the Antwerp Zoo shows that even in captivity, bonobos do not necessarily have longer swelling durations than chimpanzees. The supposed release from estrus that is said to characterize bonobos has been overstated because the data are based on captive animals.

Other aspects of bonobo behavior bear a second look as well. Female bonobos, it is true, are often dominant to males, but this domination occurs in only two settings, when either food or sex is involved. A male often gets sex by acceding to a female's desire to feed and so might be thought of as strategically submissive in select situations. Cleverness through subordination is certainly not unknown in other primate societies.

And are bonobos entirely peace-loving? About half of all the intercommunity encounters seen by Kano's team involved aggression of some sort. The difference between chimpanzee aggression and bonobo aggression is that bonobo attacks and injuries are often directed by females at males, rather than the reverse as in chimpanzees. There are even reports from zoos of female bonobos brutalizing a male so badly that his penis was severed.

Meat eating, while certainly less common among bonobos than among chimpanzees, may be under reported because bonobos are so little studied. Barbara Fruth and Gottfried Hohmann of the Max Planck Institute for Evolutionary Anthropology in Leipzig have observed extensive meat eating and meat sharing by bonobos at Lomako, but most "chimp-ologists" still refer to the bonobo as the "vegetarian" great ape.

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