It is no secret that fathers―even “new age” fathers―tend to spend less time than mothers caring for their children. It is equally well known that men tend to have shorter lives than women. That the two facts might be connected, however, is surprising. But research by John Allman of the California Institute of Technology and his colleague suggests that they are. Differences in longevity between the sexes, at least in primates, seem to depend on which parent looks after the kids and how much effort she (or he) puts into it.    Allman and his colleagues examined how adult males and females share parenting choices in ten species of primates, including humans. They then compared the male-female longevity patterns in the species. The pattern that emerged is that among primates that closely shared the care of offspring, the male and female lifespan were nearly the same. But in species in which males took almost no part in child-rearing, the females outlived the males by a wide margin.   The researchers managed to find two monkeys where the father is very new age: the titi monkey and the owl monkey. In both titi and owl monkeys, fathers carry their young from shortly after birth. Gratifying for Allman, his theory was confirmed-male titi and owl monkeys live about 20 % longer than the females of the their species. The argument that the non-care giving sex is trading more freedom for a shorter life also makes some sense, at least for males. The more “available” females are, owing to the lack of a permanent pair bond, the more they are worth competing for. Such competition is not cost-free. But if it results in extra offspring, then it is worth it, evolutionarily speaking.   That, however, suggests that female titi and owl monkeys must be involved in a life-shortening trade-off of their own. Just what this is remains unknown. But it is at least heartening to discover that natural selection has found a way to reward nurturing parents.