A comment by Keith Parsons in the followup thread to his post titled Belated Response to Ed Feser provides a good springboard for me to address myself to Ed Feser and his book The Last Superstition, now about 3.5 years old. I will do this over a series of posts; there is a lot to be said.
Feser writes (TLS, p. 36): “the Forms, as archetypes or perfect patterns, are the standards by reference to which particular things in the world of our experience count as being the kinds of things they are. A triangle is a triangle only because it participates in the Form of Triangularity; a squirrel is a squirrel only because it participates in the Form of Squirrel; and so forth.” This passage is elucidating the thought of Plato, but it seems clear that Feser (though an Aristotelian/Thomist) basically agrees.
Anyway, Parsons nails it:
Where the notion of form might be interesting but false is in postulating a form for organic species. However, such a notion is most definitely undermined by Darwinism. Where now is the form “Tyrannosaurus?” If speaking of the form “Tyrannosaurus” is only a way of referring to the temporary anatomical arrangement of a kind of theropod dinosaur that flourished at the end of the Cretaceous, then, again, such terminology does refer to something real, but is only a portentous-sounding way of stating the obvious.
If, on the other hand,“Tyrannosaurus” is supposed to designate something that exists diachronically as a permanent essence that in some mysterious way shapes or guides organic processes (and this is the only way such a concept could be interesting), then such a thing definitely does not exist, so far as biological science can tell. Organic “form” resides in the genome, which we know to be plastic, and we know why and how it changes over time. Considered over geological time, there are no species. Looked at over hundreds of millions of year, one “form” flows into another or goes extinct. Those are the only two possibilities. To account for this process, “substantial form” does not need to enter anywhere.
If Feser wants to defend the notion that it is useful or even meaningful to talk of the “Form of species s” as distinct from or metaphysically prior to “the population of species s living in region r at time t”, he has a lot of work to do.