Full Idea
The reason natural properties feature in the contents of our attitudes is that naturalness is part of what it is to feature therein. We aren't built to take a special interest in natural properties, or that we call them natural if they are interesting.
Gist of Idea
For us, a property being natural is just an aspect of its featuring in the contents of our attitudes
Source
David Lewis (New work for a theory of universals [1983], 'Cont of L')
Book Reference
'Properties', ed/tr. Mellor,D.H. /Oliver,A [OUP 1997], p.227
A Reaction
Evolution never features in Lewis's metaphysics. I would have thought we were very much built to focus on natural properties. This sounds odd, and gives no help in distinguishing natural properties from all our other daft contents.