Full Idea
It seems clear that in some cases one natural kind may be a subkind of another, while in other cases natural kinds may overlap without one being the subkind of another.
Gist of Idea
Natural kinds may overlap, or be sub-kinds of one another
Source
Alexander Bird (Philosophy of Science [1998], Ch.3)
Book Reference
Bird,Alexander: 'Philosophy of Science' [UCL Press 2000], p.111
A Reaction
Given the enormous difficulty of pinpointing natural kinds (e.g. Idea 6768), it is hard to know whether the comment is correct or not. Ellis says natural kinds come 'in hierarchies', which would make subkinds normal, but overlapping unlikely.
Related Idea
Idea 6768 Tin is not one natural kind, but appears to be 21, depending on isotope [Bird]