The Natural Selection of Unnatural Acts

Abstract

Sexis always a captivating subject for discussion, even when we are thinking of animals rather than people. We all know this, but we rarely stop to consider how profoundly our unavoidably human perspective influences our thoughts about animal sex. When members of two different species mate, we pay even closer attention, as evidenced by any number of scientific notes on mixed matings in the grey literature of natural history. Often, these papers include a photograph depicting the deviant act itself (e.g.Nordin 1985). I don't think it's much of a stretch for me to claim here that we find these events intriguing because of the general notion that animals mate according to their kinds, and the (yes, very reasonable) taboo against engaging in such behavior ourselves. Indeed, Bulletal. (2006) have pointed out that is often seen as unnatural and Dowling and Secor (1997) refer to negative attitudes toward hybridization as a major impediment to understanding this phenomenon in nature. In recent columns, I have been exploring the ways in which metaphors structure our thinking, even in science, and here we have yet another fascinating example. Evolutionary biology has long supported the notion that hybrids are mistakes of a sort. The biological species concept was, in part, based on the notion that a well-adapted genome will protect itselffrom the influence ofless well-adapted genes through the evolution ofreproductive isolating mechanisms, referred to metaphorically as barriers:' In nature, one might think, there should be safeguards against the unnatural. But what if these safeguards fail, and the barriers break down or if the genome of a species is invaded (Mallet 2005)? Are these military metaphors justified? At best, we all know that you get something mismatched and