Evolving Thoughts

Evolution, culture, philosophy and chocolate! John Wilkins' continuing struggle to come to terms with impermanence... "Humanus sum, nihil humanum a me alienum puto" - Terence

Friday, June 03, 2005

The evolution of ruling myths

It's funny how myths get started in science. As I continue to slog my way through various eras in search of the Giant Elusive Species Concept (it's in there somewhere. I can hear it rustling around), I come across what seem to be really useful sources. One of them is a classic paper by Conway Zirkle:

Zirkle, C. (1959). "Species before Darwin." Proceedings of the American Philosophical Society 103(5): 636-644.

According to him, species were not regarded as fixed before they were declared to be so by Linnaeus in the late 17th century. He adduces all kinds of sources, including Aristotle (of course), a bunch of late Classical writers, Augustine, Aquinas and so on. But I was a little bemused at the way he treated Aristotle, and so when he said "Theophrastus devoted almost an entire book (Enquiry into Plants Bk II) to describing how plants changed their species", I was suspicious. I had finished a review of how Theophrastus, the founder of botany (unless Aristotle did it first as rumour has it) and a student of Aristotle, had treated species in Book I, and it didn't seem to gel.

Off to the library, returning with the Loeb edition (Greek and English), and Theophrastus' De Causis Plantarum for good measure. [If ever I win a lottery, I intend to order the entire Loeb classical library.]

Guess what? Zirkle is, so far as I can tell, almost complete wrong. Theophrastus is concerned with how to propagate plants by seed, by cuttings, by grafting and so on, and apart from repeating Aristotle's belief in spontaneous generation, which I outline here, he is entirely sensible about it. He doesn't think plants or animals suddenly change their species (they do, of course, change their form, especially in metamorphosis). Like any good horticulturist, such stupidity is ruled out by a vast experience. Kudos to Theo...

Why the mistake? Well Zirkle is reading his sources through a particular lens - that of the post-Darwinian period. So he either has complete fixism of species (which, to be fair, Linnaeus did have, at least in the standard works; later he noted a case of speciation by hybridisation in the genus Pelor), or he has transmutation of species. But that isn't the right contrast for the material - its either a rigid fixism, or a rough and ready maintenance of kinds. Not "species"; at least not in the sense a modern would use it.

Originally, "species" was the "special" term divided out from a broader "general term" - "a genus". So both genus and species were "kind terms". Locke made the suggestion that we think of them as "kind" for genus and "sort" for species. In the middle ages and earlier, that's a pretty good translation. So if something changes from one sort to another, has it changed species? Not necessarily.

Anyway, it's fun getting into the mindsets of the ancients. And as I do, yet again, I realise they are not stupid or blind. Calling Captain Obvious...