Infanticide happens in multi male groups too such as

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infanticide happens in multi-male groups, too - such as chimps and multi-male red howler monkey troops - for the same reason: - when a new male joins the group - or when a male moves substantially up in the male dominance hierarchy - in either case, few or none of the current infants are his - killing an infant causes the female to stop lactating and start ovulating again - so the new or rising male has a chance of fathering her next infant - this is another example of selection favoring something that is harmful to the group - what increases individual males’ reproductive success - could lead the group to shrink or go extinct - evidence that supports this explanation of infanticide - new males kill infants only when they first arrive; they stop killing infants before any of their own can be born - Boyd and Silk express this same concept in a different way, noting that in numerous studies, males are shown to kill primarily infants that must have been conceived before they joined the group - as determined both by the date of arrival of the male versus the age of the infant - and by DNA tests of the males and the dead infants - note that this does not necessarily mean the males can recognize their own infants - it may just mean that they tend to kill infants when they first arrive, then taper off - new males mostly kill the young infants that are nursing, whose deaths will make their mothers become receptive quicker - they don't bother with older juveniles who are no longer impeding their mother's fertility - observations in several species show that the infanticidal males frequently do mate with the females whose infants they have killed - infanticide plays a major role in evolution of some primates - in several species, up to a third of all infant deaths are infanticides - this has a big effect on r.s. of the mothers, and of the fathers - selection presumably would favor female behaviors to minimize infanticide - mothers in some species form “friendships” with certain males after they give birth, staying near them and grooming them frequently - note that this is the exact opposite from the grooming behavior in monogamous primates - where it is males who do most of the grooming - the female is acting in a way that keeps the male around, not vice versa - the male may defend the infant from other males - presumably these “friendships” pay off for the males’ r.s. in some way - they benefit a little from the grooming, but not much
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Intro to Biological Anthro F 2011 / Owen: Sexual selection p. 9 - mostly, such friendships may tend to be between individuals who have recently mated, meaning that the infant is be more likely to the male’s own offspring - in that case, the male is increasing his r.s. by helping his own infant to survive - this investment by the male is called parenting effort - friendships may also increase the likelihood of mating in the future - this investing by the male is called mating effort - females mate with multiple males, even during pregnancy, when the male can’t actually become the father -
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