The Proximate Causes of Extinction

Abstract

The vast majority of contemporary extinctions can be viewed as anthropogenous in the sense that human activity greatly reduced population sizes and extinction would not likely have occurred now without the human activity. However, one would still wish to know why small populations, even when protected from further human interference, appear to be unusually prone to extinction. Empirical data on the last gasp of such declining species are almost nonexistent but there is evidence that four forces conspire to put small populations at increased risk: demographic stochasticity, genetic deterioration, social dysfunction, and extrinsic forces. There are presently no models that accurately apportion the threat of extinction among these forces and even the available guidelines for indicating which species are especially at risk are very imprecise.

Well, ther’ ain’t no sense in it. A body might stump his toe, and take pison, and fall down the well, and break his neck, and bust his brains out, and somebody come along and ask what killed him, and some numskull up and say, “Why, he stumped his toe.” Would ther’ be any sense in that? No.

— Mark Twain The Adventures of Huckleberry Finn