The Importance of Monkey Grandmothers

Humans are almost unique among mammals in experiencing menopause a long time before their actual death. That is, they continue living for an extended period after they cease to be able to have children and pass their genes on to the next generation. Evolutionarily speaking, one might think, there is no longer any point to them; their task is done. But, obviously, that's not the case, as we can see from the importance of grandmothers and other female elders in, for example, tribal societies. For example, their greater knowledge of the world, and the ability to share in the childcare of their descendants, can mean that the latter have a better chance of survival.

Examples of this effect among other mammals are much less common. At the extreme, some mothers simply drop dead as soon as they have raised even a single batch of children to adulthood, but even among the majority of species, it's being a mother, not a grandmother, that's really important. Perhaps the best known exception is among elephants. Here, the leader of a family group is typically the oldest living female, who helps the herd through her knowledge of the outside world (where watering holes may be found in the dry season, for example), experience of predators, and a lifetime's worth of social knowledge.

Monkey Police

Monkeys can be a pretty violent lot. They will fight over access to resources or mates, or to establish dominance, which, in the long term, amounts to much the same thing. If it works, and you get more food, or more children, or whatever you're after, that's great, but there's always a cost involved: you might not win. Or, if you do, but you get injured in the process, it may be a short-lived, Pyrrhic, victory.

So many animals avoid fighting by simply avoiding each other. They mark out territories to warn off others of their species, to say 'this bit of land is mine, and you'll keep out if you know what's good for you.' When they do face each other, one of them - usually the interloper - generally backs down before things get violent. This is fine for animals that live on their own, but it's not so great when, as with many monkeys, the animal lives in a group, where you just can't stay out of each others' way.

The group may still mark out its territory somehow, and fight off outsiders when they need to. But there is still always going to be conflict within the group, especially where the society is clearly hierarchical, and one top monkey monopolises the mates, or just gets first pick of the food. Yet, while this conflict is necessary to establish the hierarchy in the first place, and gives benefits to those who come out on top, it's not good for the group as a whole.