Evolution Explains Why Animals Kill Babies

Last night I took my lovely girlfriend out for a birthday dinner to one of those wackily-hip places with crazy neon mood lighting, a cacophony of Top 40 hits and a damn pond in the middle of the place. Ending up at a club for dinner wasn’t the worst thing in the world, but I’ll tell you what was: Hearing "Happy Birthday" sung loudly and poorly at ten other tables over the course of the night while children hopped up on caffeine and duck sauce ran around twitching and screaming like medalists at the Meth Olympics.

With little punks aurally assaulting me just about everywhere these days, I can’t stop thinking about how lions eat their kids, and wondering if that might be something us humans could learn from.

Angry ranting aside, infanticide is quite common in the animal kingdom. It’s a heavily studied topic for behavioral ecologists and ethologists, largely because it doesn’t necessarily make intuitive sense. Why would adorable gerbils, for example, actively hunt down and eat the offspring of others? What could possibly be the evolutionary benefit of becoming a ruthless baby gerbil killer, other than some peace and quiet?

The reason infanticide is such an interesting area of study—aside from the fact that there are examples in all walks of animal life—is that it refutes a pervasive misconception about the mechanics of evolution: That animals act in the interest of their species. The ‘survival of the species’ idea makes sense and has no messy morality issues. It suggests that animal behavior would be directed by a desire to propagate the species, likely in order to keep their potential mates alive.

Take the Hanuman langur in Nepal as an example. Research has found that in the langurs’ breeding groups (which contain multiple males), attacks on infants by mature males are common. Those males don’t attack their own offspring, instead, they attack the young of others. As Carola Borries writes in 1997, "Since rank and mating success were correlated and rank and reproductive success might be correlated, all attackers had a good chance of siring the next infant of the victims’ mothers and could thus have benefited by their action."

Ugly cases like this highlight the fact that evolution is an inherently selfish process, at least from a strictly mathematical, genetic point of view. In the oft-cited lion example, a male who takes over a pride is likely to kill off all of the cubs, which forces the females into heat and allows the mae to quickly spawn his own fleet of cubs. To put it bluntly, that male lion would rather kill off the young of others than waste him time and energy taking care of cubs that don’t carry his precious genes, not to mention the risk he’d face by waiting to mate with the rest of the pride.

But if its biologically valuable for lions to dump the dead weight of kids that aren’t theirs, why don’t all animals do it? Other than the fact that it’s distasteful (which probably doesn’t have much of an effect on evolutionary processes), it’s not necessarily advantageous. It’s not like killing off a whole pack of cubs isn’t extremely costly, especially when you consider those cubs mamas or papas are certainly going to defend them. For animals who don’t keep to competitive mating groups, like raccoons, the cost of raiding a well-hidden and defended nest to kill the kids of a random individual far outweighs the minute potential benefit gained by slightly increasing the odds that they might mate with that individual.

Which brings us back full circle to the screamy little kids at dinner. Even if their poor parents refuse to admit that the youngsters are made from their own genetic material, they don’t get rid of them because the costs of dealing with the legal and emotional ramifications are unlikely to be outweighed by the benefits of any more sex. But it also has nothing to do with this ‘survival of the species’ funny business, because, let’s be honest: these pint-sized lunatics are slowly killing me.

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