A male monkey cruising through the grasslands with a harem of females all to himself might seem to have hit the primate jackpot. What simian doesn't want a dozen lady monkeys to bear his long-tailed young and then tote them around? But he's better off sharing the wealth. By letting other males infiltrate his group and mate with his females, the leader lands himself a longer term in office—and more, not fewer, of his own offspring.
The gelada (pronounced not unlike the Italian frozen dessert) is a social animal that lives only in Ethiopia. Males have luxurious hair capes and bright red hourglass shapes on their chests. The lucky ones live in groups called reproductive units that include one "leader" male and up to twelve females. About a third of reproductive units also include one or more "follower" males.
Unattached males, meanwhile, live in bachelor groups that wait for the ...
