Subordinate adult male WBH holds his probable infant offspring in the presence of alpha immigrant male WNR, in foreground yawning and consorting fully-swollen female WEM. The infant's mother is not in the photo.
By the late 1970's the behavior and social organization of savanna-dwelling baboons had already been well documented at multiple sites, especially in East Africa. Less was known about the Chacma baboons of Southern Africa, and after just two years at a new site in the Okavango Delta, we made a major new discovery: adult males protect their infant offspring from potentially-infanticidal immigrant males.
The conventional wisdom was that adult male baboons provide little direct care to young because of the assumed low confidence of paternity inherent in groups containing many adult males. Also, on rare occasion male baboons had been observed killing infants, but no one had suggested that infanticide might be a feature of these societies, as found by Sarah Hrdy for single-male groups of langur monkeys in India.
We reported our findings in Science; the two-page article, accompanied by Bill's cover photo, was the first to identify infanticide and protection of infants as key elements of male life history strategies for any primate living in multi-male groups. The study revealed that male Chacma baboons - despite the seemingly promiscuous mating system - often act as if they are aware of paternity, as evidenced by their protection of probable offspring against non-fathers.
Scientists working in East Africa did not generally greet our report with open arms (despite our friendly challenge in the last paragraph). More than 20 years later, the consensus is that Chacma baboons, for various reasons, are much more prone to infanticide than are their sibling species (Note 1). And whereas the relationships among adult males, infants, and their mothers are well understood for Chacmas, the picture from East Africa is still a bit of a puzzle.
After Curt left the Okavango, Bill and his student John Bulger continued this line of investigation and made many additional new findings consistent with the basic pattern. Our understanding of infanticide and its implications among the Okavango baboons has also been greatly advanced by recent studies led by Ryne Palombit, who found, among other things, that infanticide accounts for more than a third of infant mortality.
With evidence continuing to accumulate from the Okavango and other sites throughout Southern Africa, the exciting discoveries that we reported in Science in 1981 have become an integral part our basic knowledge of the sociobiology of Chacma baboons.Curt Busse and Bill Hamilton
R. A. Palombit. 2003. Male infanticide in savanna baboons: Adaptive significance and intraspecific variation. In: Sexual Selection and Reproductive Competition in Primates: New Perspectives and Directions (C.B. Jones, ed.), pp. 367-412. American Society of Primatologists.
P. Henzi and L. Barrett. 2003. Evolutionary ecology, sexual conflict, and behavioral differentiation among baboon populations. Evolutionary Anthropology, 12: 217-230.
M. Broom, C. Borries, and A. Koenig. 2004. Infanticide and infant defense by males - modeling the conditions in primate multi-male groups. Journal of Theoretical Biology. In press.