Metaphysical investigation often proceeds by way of linguistic meaning. This tradition relies on an assumption about meanings, namely that they can be given in terms of referential relations and truth. Chomsky and others have illustrated the difficulty with this externalist hypothesis regarding natural language meanings, which implies that natural languages are ill‐suited for the purposes of metaphysical investigation. In reply to this discordance between the features of natural languages and the goals of metaphysical investigation, metaphysicians propose that we look to (...) the invented languages used to express our best scientific theories as metaphysical guides, in the hope that these languages are better behaved. I argue that this retreat is beset with similar troubles for the metaphysician. In particular, I argue that central terms in the field of biology, namely ‘gene’ and ‘species’, exhibit a kind of lexical flexibility that renders them, much like their natural language counterparts, ill‐suited for the metaphysician's aims. (shrink)