When is it co-evolution? A reply to Steen and co-authors

Abstract

David Steen and co-authors in this journal offer a philosophical argument to support an “Evolutionary Community Concept” to identify what they call “evolutionary communities.” They describe these as “unique collections of species that interact and have co-evolved in a given geographic area” and that include “co-evolved dependencies between different parts of a community.” Steen et al. refer to the coevolution of assemblages, collections, communities, dependencies, interspecific and abiotic interactions, and traits, but they do not define “co-evolution” or provide an example in which co-evolution (as distinct from interaction) has been demonstrated. There may be as many ways to explain interactions among species as these interactions themselves; they may result, for example, from ecological fitting and phenotypic plasticity. In this paper, I argue that standard Darwinian Theory explains intraspecific microevolution or descent with modification within an interbreeding and potentially continuous population. The power, mechanism, or force that causes interspecific co-evolution, especially at the community scale, requires further explanation.