Both species, humans and chimpanzees, can be extremely territorial, and territorial disputes between groups can turn violent, with individuals killing each other. In humans, such between-group competition can escalate to war and devastating loss of human life. Researchers from the Max Planck Institute for Evolutionary Anthropology studied wild Western chimpanzees to find out whether territorial behavior may have shaped counter-strategies. One important strategy that is evident in both humans and chimpanzees, but rare in the rest of the animal kingdom, is the capacity to work together in order to achieve a goal, for example to defend a territory - even if it is together with individuals who are not one's kin.
The researchers tested whether the effects of territoriality - the pressure that neighboring groups exert on each other on one side, and the competitive capacity of a group on the other side - impact female reproductive success. Reproductive success is a measure of how many of one's genes pass into the next generation and therefore how much of an influence one's traits have on subsequent generations. Using long-term data on four neighboring chimpanzee communities that span several decades of these animals' lives, the researchers show that between-group competition has negative effects on wild female chimpanzees' reproductive success. Competition between groups seems to have a selective impact and could have helped shape associated traits in this species.
We developed a new index of neighbor pressure that reflects the danger of intrusion by neighboring groups into one's territory. We show that high neighbor pressure during the time when females are supposed to resume reproduction is associated with a delay in reproduction, leading to longer intervals between births. We also show that having many males in a group is advantageous and speeds up reproduction". Sylvain Lemoine, first author of this study Related Stories
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