Full Idea
Explanatory significance, hence naturalness, comes in degrees: positing some kinds may be very explanatory, positing others, only a little bit explanatory, positing others still, not explanatory at all.
Gist of Idea
Some kinds are very explanatory, but others less so, and some not at all
Source
Michael Devitt (Natural Kinds and Biological Realism [2009], 4)
Book Reference
Devitt,Michael: 'Putting Metaphysics First' [OUP 2010], p.202
A Reaction
He mentions 'cousin' as a natural kind that is not very explanatory of anything. It interests us as humans, but not at all in other animals, it seems. ...Nice thought, though, that two squirrels might be cousins...