Full Idea
An intrinsic essence does not have to be 'neat and tidy'. ...Essentialism can accept the gradual change of one thing into another.
Gist of Idea
Things that gradually change, like species, can still have essences
Source
Michael Devitt (Resurrecting Biological Essentialism [2008], 11)
Book Reference
Devitt,Michael: 'Putting Metaphysics First' [OUP 2010], p.248
A Reaction
My thesis is that essentialism is a response to the needs of explanation, so as long as there is some core explanation to be found, even in something transitory, then the concept of an essence can apply to it.