In his The Species Problem, Biological Species, Ontology, and the Metaphysics of Biology , David Stamos explores various theories of species, and concludes that none of the existing theories suffice. In their place, he proposes, drawing on but modifying the work of Bertrand Russell, a relational view of species.

This is over against “species nominalism,” the view that “biological species are not objectively real-real in the sense of extra-mental-that they are fictions. Normally on this view only individual organisms are real” (21). It is also over-against the view that species are classes: “The primary position here is the view which conceives of biological species in the same way as natural kinds in chemistry, fundamentally as chemical elements in the periodic table of elements. On this view natural kinds are spatiotemporally unrestricted with kind membership determined by necessary conditions jointly sufficient for membership” (22). And it is also over-against “species essentialism,” a view with a long tradition stretching back to, Stamos says, Genesis, Plato, and Aristotle.

He lays out the species-as-relation view:

“assuming that it is true that relations require relata for their existence, that there can be no pure relations-indeed I go so far as to say that the relata are part of what a relation is-it follows that in referring to real relations one is also referring to their relata. But it by no means follows that one is only referring to their relata. One is referring to their relata plus something more. It is that something more that is missed not only by the species nominalists but also by the realists who place their focus only on properties or on the organisms themselves. It is also missed by the remainder of the realists since they employ some relations but that employment is marginal and normally restricted in focus to no more than one kind of relation. In saying that species are relations, I mean that when biologists correctly delimit species and when the rest of us correctly use species words (the words themselves, of course, are entirely arbitrary) we are all in effect referring neither to entities abstract or concrete nor to their members or parts; instead we are referring to the individual organisms and the relations between them that together constitute their reality as species. Their reality, then, is neither strictly abstract nor concrete, but is a sort of hybrid between the two. And it is because relations have not only a different ontology but also different existence conditions from both classes and physical entities that they make the most suitable candidates for the constituents of evolving species in the biological world. In short, I shall argue that thinking of species as relations leads to the novel view that a species is a complex of similarity relations (with organisms ultimately as the relata) objectively bounded or delimited by various causal relations (such as interbreeding relations, ecological relations, ontogenetic relations, caste relations, etc.)” (25).

Though Stamos classifies the Bible as a “species essentialist” text, and though that is the way the Bible has often been read, I think it’s a one-dimensional reading of the creation account. To be sure the Bible speaks of “kinds,” but also points to created relations with environments (sea, land, sky) and relations to other kinds that inhabit the same environment (land animals and humans, for instance, both made from dust). The classifications in the dietary laws seems to be similar to his notion of “complex of similarity relations.”