Historian Mary P. Winsor published recently (2006b, in the December 2006 edition, but it just came out) a paper discussing how the Essentialism Story was constructed by Arthur Cain, Ernst Mayr, and David Hull.
The Essentialism Story is the claim that before Darwin systematists and biologists in general treated natural kinds such as species as being defined by necessary and sufficient conditions. That is, to be a member of a species, an organism has to have all the right properties. After Darwin, goes the story, "population thinking", which denies that there are such necessary properties.
Polly (she prefers to be so called) argues that this was based on Mayr's hatred of Plato, Hull's reading of Popper, and Cain's dismissal of Aristotle. In fact, she (and I) think that systematics practice was not at all based on metaphysics, but on good empiricism and she terms her replacement view "the empiricism story". Recent work by Staffan Müller-Wille (in press) on Linnaeus verifies this - Linnaeus, who is supposed to be the bad boy with typological essentialism, in fact was pretty good at empirical observation. Polly also has another paper (2006a) on Linnaeus, pointing out what should be fairly obvious: Linnaeus never did Aristotelian classification by division.
It's an interesting paper not online, unfortunately, as it deals with how scientists do history and why - it's a "metahistory" paper. But what tickled my fancy more than anything else is that Polly cited my PhD dissertation. W00t!
Winsor, Mary P. 2006a. Linnaeus' biology was not essentialist. Annals of the Missouri Botanical Garden 93 (1):2–7.
Winsor, Mary P. 2006b. The Creation of the Essentialism Story: An Exercise in Metahistory. Hist. Phil. Life Sci. 28:149-174.
Although my paper in History and Philosophy of Life Sciences is not online, I will be glad to email a pdf or mail hard copy to anyone who wants a copy. Same goes for the Missouri Botanical Garden paper and the one on Cain. Just ask: email@example.com
I picked up on Mayr's attitude to Plato and essentialism in "One Long Argument", which I still think is a good book.
Did Mayr also get this antipathy to Plato from Popper? Popper's "The Open Society and its Enemies" is the most famous modern attack on Plato, though on political rather than scientific grounds.
According to Polly, Mayr got it from his childhood education in Germany. There is a strong German biological tradition of ideal morphology based on Platonic/Goethean ideas. So far as I can tell from his published work (and also from a paper by Charles Chung a few years back) Mayr never read Popper until quite a bit after the Essentialist Story was complete, and then only in terms of confirmation theory.