According to a documentary released by Disney in 1958 called White Wilderness, it was revealed that lemmings (small rodents) committed mass suicide, in showing footage of them jumping off a cliff. However, nothing could be further from the truth as the footage was faked due to the fact that the filmmakers pushed them off a cliff while not being in the footage themselves.
Until now, it has been considered that lemmings were ‘suicidal’ by nature, and it was assumed that it was this bizarre behavior that attributed to the large population drop (which often brings the species to extinction) that occurs every four years.
Scientists find it hard to believe (the theory) of mass suicide committed by lemmings for the greater good, just so that the species would be able to survive on the food supply, since this behavior could never evolve in practice especially amongst species of animals.
Charles Krebs, from the University of British Columbia, seems to have come up with a more workable explanation for this odd behavior of lemmings that occur every four years. While a food shortage can kill the population, there has been no data to substantiate this for lemmings.
Another probable factor would be the presence of predators due to presence of a large population of lemmings, and while this might be one of the factors that Krebs thinks effects the numbers every four years, the conclusion that he has come to is that male lemmings commit infanticide, which is killing pups that are not their own, but of other males.
One reason why this explanation might work is because this ‘predatory’ behavior has been seen amongst species of lions and chimps as well, and while selflessness is not necessarily something animals are capable of, perhaps the explanation where male lemmings kill the offspring of other males seems to be a plausible one.