Lemmings. They jump off cliffs, en masse, following each other toward certain death.
Ok, not really. The mass suicidal behavior of lemmings is a myth. They do no such thing.
The basis for the misunderstanding? First, lemmings live near the Arctic but do not hibernate. Instead, they are constantly foraging for food, even in lean (and very cold) winter months. Often on the move and traveling in large groups, the law of averages takes over: a percentage of them are going to succumb to tragic deaths — falling into rivers, off cliff-sides, etc. Second, every four years, the lemming population takes a dramatic plunge (pardon the pun), approaching near-extinction levels. Combined, we get a neat — but untrue — old wives’ tale: that lemmings keep their population in check by following each other into committing suicide.
But evolution holds that this cannot be true. The surviving lemmings simply wouldn’t have the genes which made them predisposed to mass suicide; therefore, the behavior would wane with each passing generations, and finally disappear after a while. But the lemming population still goes through the same quadrennial boom or bust cycle. Mass suicide simply isn’t the reason.
The most common theory — predators — sadly is not as interesting. The theory holds that predator activity reaches a tipping point in the fourth year; as the lemming population hits its high point, so therefore does the abundance of easily attainable food for those who prey on lemmings. In this scenario, the feast is so devestating to the lemming community that for the three years following, there are not enough of them to attract a meaningful number of predators.
But recently, another theory — one more worthy of the lemmings’ self-destructive reputation — has surfaced, albeit in a laboratory setting. A new study shows that male lemmings will kill the infants of other lemmings, with a greater likelihood of lemming infanticide as population density rises.
And nota bene: while mass sucide is inconsistent with evolution, infanticide is not.
From the Archives: Early Warning Lemurs: Different animal but sounds close enough to “lemming” to be worth including here.