Natural Kinds and Genetic Lines

Will Wilkinson writes:

You are not an instance of a natural kind. You are a member of a genetic line. You have no essence.

He asserts
till it hurts.

To back it up, he links to a paper in which the author, near the end, says:

In fact I think that the species category may very well be a natural kind and that part of its essence is variability.

So the cite
doesn't quite
back
his attack.