Eating The Kids

All in the family sounds pretty cozy, but things are not always as simple as it sounds when we are out in the wider world of birds and animals. The old fella, the patriarch, sooner or later will be found lacking and there will be a new sheriff in town.

The bad news then is that often the young offspring will end up as a meal and the new guy will be ready to stamp his genes on the future generations. Infanticide is more common than we like to think when we watch the cuddly babies in the zoo or on our TV screens.

It is not just the new alpha male that indulges in infanticide, but some females do this as well and, unless there is a period of severe deprivation, the logic seems to go against the survival interests of the group, but is it?

Lyon et al worked as a team of biologists, anthropologists and physicists on this problem and published their deliberations in the J. of Theoretical Biology (1,2). Their high level thoughts focused on primates and with idle computers on their hands, they decided to play a three-player game with one female and two males – a new guy and an old guy.

In the game the female can decide to mate with either or both males and there is an underlying assumption that she will be interested in avoiding infanticide as she will have put a fair bit of effort into her young family. After a great deal of electrons rushing about, the result came back that under some conditions a promiscuous female could safeguard her youngsters by mating with both males so that their idea of parenthood was a little blurred.

However, this only works under a limited range of conditions. They found that eating the kids was a common strategy when the times were turbulent with incoming strong guys coming in to take over.  Their conclusion was that infanticide was the probable outcome when the new guy knew that the next generation that he was about to start would clearly be his.

This study was aimed at primates and I guess that the great apes were in the forefront of the thoughts of the authors, but it has echoes throughout world history. I guess that the old saying “it’s a wise child that knows its own father” must stem from times when things were quite and not too turbulent.


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