Sandefur on Essences in Nature:

Timothy Sandefur has replied to DHS's comment refuting the notion that "essences" are found in nature. Sandefur focuses in on Ayn Rand's and Daniel Dennett's teachings to save naturalistic ethics from the death of essentialism.

Also, Jason Kuznicki has a great post reacting to my initial post, with some excellent comments. I'm glad I generated so much thoughtful reflection.