Dear Straight Dope:
Does any animal, other than the human species, commit suicide?
If you mean, "Other than humans, do otherwise healthy and reproductively-capable individuals of any other species perform actions foreseeably guaranteed to result in their immediate death?", the answer is NO. Violate any one of the conditions in the preceding statement, and the answer is YES. Sick or injured animals of many different types will act in such ways as to guarantee a speedier end to their suffering, and this appears to include whale beachings. Whale beachings are also one reason for the qualifier "foreseeable," in that it appears healthy whales may follow a sick leader when the latter beaches–as social animals, they instinctively trust their leader, which under most circumstances would not lead them to their doom, so their unexpected (to them) beaching cannot be considered genuinely suicidal. For that matter, a rabbit that walks out into an open field when there’s a hungry owl nearby may be performing an action virtually guaranteed to result in death–but not foreseeably so. Nor would an animal that dies defending its young necessarily be considered suicidal, even if the enemy is something pretty much impossible to defeat; after all, the enemy might retreat if it doesn’t seem worth the trouble, so sometimes defense works.
The reason for the clause "reproductively-capable" is that there are many social insects with sterile, suicidal soldiers or workers–for example, termite soldiers that explode their bodies, which are filled with sticky guts, immobilizing their enemies in goo. As a final note, the stuff about lemmings jumping off cliffs, of course, is a myth.
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