Full Idea
What is sufficient in the inward contrivance, to make a new species? There are some watches, that are made with four wheels, others with five. Is this a specific different to the workman…in the internal constitution of watches?
Gist of Idea
Internal constitution doesn't decide a species; should a watch contain four wheels or five?
Source
John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 3.06.39)
Book Reference
Locke,John: 'Essay Concerning Human Understanding', ed/tr. Nidditch,P.H. [OUP 1979], p.463
A Reaction
It so happens that most species turn out to be internally very similar, but Locke is right that it might not be the case.