Full Idea
There are sorts or species such that if an individual has ever been of such a sort or species it cannot (naturally, at least) stop being of it.
Gist of Idea
For some sorts, a member of it is necessarily a member
Source
Gottfried Leibniz (New Essays on Human Understanding [1704], 3.06)
Book Reference
Leibniz,Gottfried: 'New Essays on Human Understanding', ed/tr. Remnant/Bennett [CUP 1996], p.305
A Reaction
Note the thoughtful 'naturally, at least', which blocks genetic engineering. But natural selection is genetic engineering. Crucially, Leibniz is not attributing this to all sorts or species, and allows exceptions.
Related Idea
Idea 12906 Truths about species are eternal or necessary, but individual truths concern what exists [Leibniz]