Animals are rarely known for their suicidal tendencies. Perhaps because when your daily thought pattern is limited to eat-sleep-defecate, there's no time for existential exegesis or contemplating the futility of life. That is, except for the lemming—a small, furry, gerbil-like rodent that has come to be defined by its alleged tendency to mindlessly kill itself by jumping off of cliffs. However, the long-lived myth actually has its roots in Hollywood trickery.
Populations of lemmings fluctuate dramatically, from massive herds to near extinction. For years, theories on these populace peaks and plummets varied from the supernatural to the absurd.
"In the 1530s, the geographer Zeigler of Strasbourg, tried to explain these variations in populations by saying that lemmings fell out of the sky in stormy weather, and then suffered mass extinctions with the sprouting of the grasses of spring. Back in the 19th century, the Naturalist Edward Nelson wrote that 'the Norton Sound Eskimo have an odd superstition that the White Lemming lives in the land beyond the stars and that it sometimes comes down to the earth, descending in a spiral course during snow-storms.'"
That was before the modern meaning gained traction: That populations tumbled because packs of lemmings would occasionally run head-first off of cliffs, plunging to their self-induced death for no apparent reason. To refer to an individual as a lemming thus became synonymous with calling them a follower of a large group--a community on an unthinking course towards mass destruction.
However, this does a disservice to these cuddly hamster-lookalikes.
It turns out that there is no proof that an assemblage of wild lemmings would actually drive themselves off of a cliff at all, but rather the myth was perpetuated by a 1958 documentary called White Wilderness, in which the film-makers manually ran a pack of lemmings off of a cliff to make for good television. The staged suicide turned out to be a critical success, as the movie went on to win the Academy Award for Best Documentary Feature.
During the cliff-diving sequence, the pocket-sized creatures cascade into thin air, tumbling backward and flailing before they land with a distinctive splash in the Arctic Sea. The survivers then swim deeper into the vast body of water, where the narrator speculates they will soon drown.