The "species problem" has haunted biologists and philosophers at least since Darwin. One might well imagine that there was nothing original to say. Not so. John Wilkins attacks the popular biospecies concept, noting the problems it poses for non-sexual species and posing an alternative based on "the intrinsic mechanisms that keep taxa distinct in their clades." Thomas Reydon applies principles of self-organization, already articulated at the level of organisms, to the species level. Finally, Charisma Varma offers a new framework based on traditional mererological arguments (about ships, notepads, etc.) for the persistence of identity over time, but applied to biological species.

John Wilkins, The Walter and Eliza Hall Institute of Medical Research
"How to Be a Chaste Species Pluralist-Realist: The Origin of Species Types"

The biological species (biospecies) concept applies only to sexually reproducing species, which means that until sexual reproduction evolved, there were no biospecies. On the universal tree of life, biospecies concepts therefore apply only to a small number of clades, notably plants and animals. I argue that it is useful to treat the various ways of being a species (species types) as traits of clades. By extension from biospecies to the other concepts intended to capture the natural realities of what keeps taxa distinct, we can treat other types as traits also, and so come to understand that the plurality of species concepts reflects the biological realities of monophyletic groups. We should expect that specialists in different fields will tend to favour those concepts that best represent the intrinsic mechanisms that keep taxa distinct in their clades. I will address the question whether modes of reproduction such as asexual and sexual reproduction are natural classes, given that they are paraphyletic in most clades.

Thomas Reydon, Leiden University
"Species and Self-organization"

The concept of species plays a fundamental role in biological explanation on two distinct ontological levels: the level of individual organisms (as sets of structurally similar organisms) and the level of clusters of organisms. On the former level explanation of organismic structures in terms of self-organization and attractors in morphospace, complementary to explanation by means of natural selection, presently constitutes a flourishing research program. I argue that this kind of explanation should also play an important role on the latter level, complementary to explanations in terms of historical events, and I explore the possibility of interpreting species as attractors in a "cluster space".

Charisma Varma, University of Calgary

forthcoming