Full Idea
Kripke makes the origin of an organism essential to it, according to Putnam the fundamental physical properties of a thing are essential, Wiggins sees an organism's essence in belonging to a particular kind, etc.
Gist of Idea
For Kripke, essence is origin; for Putnam, essence is properties; for Wiggins, essence is membership of a kind
Source
report of Saul A. Kripke (Naming and Necessity lectures [1970]) by Thomas Mautner - Penguin Dictionary of Philosophy p.179
Book Reference
Mautner,Thomas: 'Dictionary of Philosophy' [Penguin 1997], p.179
A Reaction
This is helpful for seeing where the problems remain, if you embrace essentialism (as I feel inclined to do). It is vital to remember Putnam's point, that we could suddenly discover that cats are alien robots. This seems to undermine Kripke and Wiggins.