Biochemical Kinds

Chemical kinds (e.g. gold) are generally treated as having timelessly fixed identities. Biological kinds (e.g. goldfinches) are generally treated as evolved and/or evolving entities. So what kind of kind is a biochemical kind? This paper defends the thesis that biochemical molecules are clustered chemical kinds, some of which–namely, evolutionarily conserved units–are also biological kinds. On this thesis, a number of difficulties that have recently occupied philosophers concerned with proteins and kinds are shown to be resolved or dissolved.