Date of Completion


Embargo Period



species, individual, natural kind, essentialism, de-extinction

Major Advisor

Crawford L. Elder

Associate Advisor

Thomas Bontly

Associate Advisor

Samuel C. Wheeler III

Associate Advisor

Kent Holsinger

Field of Study



Doctor of Philosophy

Open Access

Open Access


The individuality thesis, or “species-as-individuals” (SAI), is the dominant view in philosophy of biology. Biological species are not natural kinds, but individuals. This dissertation defends SAI against recent proposals to reconceptualize species as natural kinds. I argue that, despite criticisms, the preponderance of considerations still weighs in favor of SAI. I then defend another consensus view in philosophy of biology, that species have no essential intrinsic qualitative properties (species anti-essentialism), against recent attempts to revive essentialism, and show how SAI is better suited than the view that species are natural kinds to defeat essentialism. I next develop an account of how it is that biologists can make reliable inductive inferences about species – in particular, reliable generalizations – given that species are individuals. One motivation for reconceiving species as natural kinds is to provide a philosophical grounding for these inductive practices, since the traditional view is that natural kinds, with their essential properties, are uniquely suited for grounding inductive inference. My account appeals to the causal processes which produce the degrees of uniformity and homogeneity within species which permit biologists to make reliable generalizations; shows that other sorts of natural kinds are also at work grounding such inferences; and argues that the inferences in question demand only that species have stable, but not essential, properties. Finally, I apply SAI to a controversial prospect in conservation, the resurrection of extinct species by cloning (de-extinction). The received view is that once an individual is lost, it cannot be recreated. I argue that the descent relation which makes offspring part of the same species-individual as their parent(s) holds between clones and their progenitors; thus clones of organisms from an extinct species are part of that species. This makes a resurrected species a temporally discontinuous object; I give reasons to think there can be and are such objects. One argument in favor of SAI is that evolutionary theory requires the spatiotemporal continuity of species, which appears to be violated here. I maintain that evolutionary theory requires the historical continuity of species, which is upheld on my account of de-extinction.