This article is about a rather interesting concept proposed by the authors called "exaptation". Traditionally when we look at functional character traits of a species, we consider them adaptations. In other words, we assume that the traits were favored because of their useful function, and therefore, selected for. It is important to understand that the word "adaptation" is the combination of the Latin "ad" + "aptus", which means "towards a particular fit." However, Gould and Vrba ask, what if there exists a trait which is functional, but was not selected for its ability to perform that functional task? Is that an adaptation? In other words, its primary function is the side effect of another adaptation.

For example, the authors discuss the feathers and the wings of a bird. Clearly, one-forth of a wing will not do much good, and it certainly will not allow flight. So then, how did birds develop the ability to fly from being wingless, flightless creatures, to the aviators they are today? According to the authors, the evolution of the wing was for reasons entirely different than for flight. The wing likely evolved as a means to catch insects. Those creatures with longer and more flexible appendages could more easily snag insects. Feathers, on the other hand, evolved as insulators like hair.

Over time the exaggeration of these functional traits lead to the ability to fly. However, this is not adaptation because because wings and feathers did not evolve to perform the function of flight, as the definition of adaptation would demand. The authors propose the word "exaptation" to account for such evolutionary traits. Exaptation is composed of the Latin "ex" meaning "form", and "aptus" meaning "fit". Therefore, it means "fit by reason if their form."

This definition explains traits that are functional for tasks by their form alone, not necessarily as a result of selection. Another example is the human hand and its ability to write. Certainly we did not evolve fingers to hold pencils and pens. However, a side effect of manual dexterity, which was selected for reasons other than writing, has given us the ability to write. As a result, our ability to write is an exaptation of the human hand. This term seems very useful in that exaptation seems to have a widespread influence in evolutionary traits. I am surprised I have not encountered the term and/or concept already.