The phrase "battle of the sexes" applies pretty literally to the Assam macaques of southeastern Asia. During mating season, males become extremely aggressive, and females rely on various tactics to defend themselves... including all having sex at the same time.
In many species, males want to both maximize the amount of children they have and ensure that their mates' children are really theirs. This sets up a couple of completing impulses - to have as many children as possible, the males need to mate with as many females as possible. But if all the males are taking on multiple partners, then it becomes extremely difficult for any male to know which child is theirs.
That's the basic situation for Assam macaques, which live in populations of roughly three dozen monkeys, of which there are a dozen each adult males and females. The mating season lasts from October to January, and males tend to get more and more aggressive as the season progresses. Part of that might well be reproductive frustration - because females don't show any outward signs of fertility, and they mate at all points of their menstrual cycle, there's never any guarantee that sex will result in conception.
This leads to some serious confusion among the males as to who fathered which baby, and that has some serious benefits for the females and the population as a whole. Unlike in species where every father knows for certain which child is his, male macaques don't go around killing other males' offspring. What's more, males actually take on the bulk of the child-rearing responsibilities. For all their mating season aggression, male Assam macaques actually turn out to be pretty good dads, if somewhat inadvertently.
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http://io9.com/5852912/macaques-use-synchronized-sex-to-keep-alpha-males-at-bay