intra-community killing, perhaps by Zimba. Unfortunately it was not possible to
preserve a sample from this infant for genetic analysis.
Two better documented cases were reported on by Hamai et al. (1992). These
occurred in the M Group of the Mahale Mountains chimpanzees. In both cases the
infants were male, 5–6 months of age, and in good health when killed. Their mothers
had immigrated into M Group 4–5 years previously as nulliparous females, i.e. they
were not new immigants. In both these cases the infants were killed by the alpha male
and there was considerable competition between the adult males of the community for
a share of the meat.
These two were among seven cases at Mahale reviewed by Hamai et al. In all cases
the infants were male. Most were completely eaten, with competition for the meat by
both adult males and adult females. The head was always eaten, in contrast to the situa-
tion in Budongo where the head was not eaten in the two cases where the carcass was
recovered.
The authors noted that only infants of immigrant females were killed. Four of the
seven mothers were young and primiparous. After considering a number of reasons why
they should have been killed, the authors concluded that
The common feature through the seven cases of within-group infanticide is that mothers of
victimized infants mated more with older adolescent and other immature males rather than with
fully adult males before they gave birth to victims....We suggest, therefore, that one function of
infanticide might be to...coerce her [the mother] into more restrictive mating relationships with
adult males and high-ranking males.In other words, females who mate with the lower ranking or less mature males in the
community run the risk that their infants will be killed by the more mature and higher
ranking males. To the extent this is true, it shows that the males in the community, even
though they live their lives together without emigrating and consequently know each
other well, are highly competitive when it comes to mating and reproduction. We have
already noted this fact when we considered mating strategies (Chapter 6). It also makes
genetic sense for, surprisingly, males are not as highly related to one another within
a community as might be expected, the genetic variation coming about as a result of the
new genes brought in by immigrants (see Appendix C on the genetics of the Sonso com-
munity). And finally this competition between intra-group males helps to explain
an anomaly we examine in the next chapter in which I describe the killing of a low
ranking, young, virile male in the Sonso community by his older, senior peers.
The role of females in cases of infanticide
Information on an active role for females in infant killing is sparse compared with that
on males. At Budongo, we have two cases of females found carrying infants that may be
infanticide victims: the cases of Kalema (December 1993) and Zimba (February 2000)
The role of females in cases of infanticide 151