The consensus in philosophy of biology is that biological essences, such as the essences of species, are wholly relational; Michael Devitt argues that they are at least partly intrinsic. He further argues that an individual is essentially a member of its species. He concludes by considering whether race is biologically 'real'.

Biological Essentialism addresses three main issues. The first concerns the essences (natures, identities) of biological taxa, particularly species. Kripke and other metaphysicians hold that these essences are (at least partly) intrinsic, underlying, probably largely genetic properties. This view, based largely on intuitions, is dismissed by the consensus in the philosophy of biology as being incompatible with Darwinism and reflecting ignorance of biology. Biological Essentalism argues that the demands of biological explanation show that the metaphysicians are right. The positive view of the consensus is that the essences are wholly relational: taxa must have certain histories. Biological Essentialism argues that there is indeed an historical component to the essence, but this component presupposes an intrinsic component. Its second issue concerns the essences of biological individuals. Metaphysicians have had much to say about this, again on the basis of intuitions. Many hold that an individual is essentially a member of its species. This has recently been unequivocally rejected by philosophers of biology. Biological Essentialism appeals to biological explanation again to argue for essential membership; furthermore, to argue for the Kripkean view that an organism's essence is partly intrinsic and partly relational (a matter of origin). Finally, the book addresses the lively contemporary issue of whether race is biologically “real”. From the perspective developed earlier, the book argues that there are indeed racial kinds, in some sense, that are “in the realm of the biological”. These kinds also have partly historical and partly intrinsic underlying essences.