"Species" in the Stanford Encyclopedia updated

Marc Ereshfsky's entry on "Species" in the Stanford Encyclopedia of Philosophy has been updated, though not to remove the classic "Essentialism Story" that has been called into question by a number of scholars lately. Under the fold, I will quote Marc's comments and critique them. [I can do this because Marc is a hell of a nice guy, and not at all precious about such stuff, at least not so far. I will test him, though. I should stress that Marc is not the originator of the Essentialist Story - it was developed between 1958 or so and 1982 largely by Mayr.]

Since Aristotle, species have been paradigmatic examples of natural kinds with essences.

Actually, no. Aristotle never spoke of what we would call species except when using terms like genesi which were vernacular terms for kinds, not specifically biological kinds. Aristotle's use of eidos, or "form" he derives from Plato's discussions, and it is not like a biological species. He talks of gene of eyes, of bees, of sponges and so forth, but it is clear that when eidos is used, he means the form of an organism, not the species of which is is a member or instance, as Plato might have.

Moreover, at no point from Aristotle, including him, to the 18th century does one find naturalists talking about "essences" with regard to organisms or species, and when essence does play a role, it is of parts, usually generation-related parts, of organisms.

An essentialist approach to species makes perfect sense in a pre Darwinian context. God created species and an eternal essence for each species. After God's initial creation, each species is a static, non evolving group of organisms. Darwinism offers a different view of species. Species are the result of speciation.

Again, this is false. No Darwinian (and certainly not Darwin himself) mentioned that essences were to be dropped, or even mentioned essences. "Types", which were distinct at all times in the logical literature from essences, were neither dropped by Darwin (how could they be? He was a member of the committee that regularised the use of types in the Strickland Rules of 1842) nor by any post-Darwinian naturalist. Julius Sachs, for example, in 1875 in his magisterial History of Botany attacks Linnaeus for his dryness and rigidity, but never for the use of essences. In fact, the first use of essentialism as an argument against species change I can find is in 1895 in Richard Clarke SJ's Manuals of Catholic Philosophy volume on Logic, well after Darwin.

Fixity of species was not, as the Essentialism Story has it, a matter of metaphysics. Nor was it, as Ron Amundson and Staffan Mülle-Wille argue, the result of empirical experience of stasis in species. This experience was available as Linnaeus knew it for over a thousand years without it becoming obvious either that species were fixed, or that they had an essence. Instead, fixism is due, in my opinion entirely, to the piety and literalism of John Ray and Linnaeus. And what is more, it was never argued for, but merely stated as a fact all knew from Revelation.

Ereshfsky continues

No qualitative feature — morphological, genetic, or behavioral — is considered essential for membership in a species. Despite this change in biological thinking, many philosophers still believe that species are natural kinds with essences. Let us start with a brief introduction to kind essentialism and then turn to the biological reasons why species fail to have essences.

Kind essentialism has a number of tenets. One tenet is that all and only the members of a kind have a common essence. A second tenet is that the essence of a kind is responsible for the traits typically associated with the members of that kind. For example, gold's atomic structure is responsible for gold's disposition to melt at certain temperatures. Third, knowing a kind's essence helps us explain and predict those properties typically associated with a kind. The application of any of these tenets to species is problematic. But to see the failure of essentialism we need only consider the first tenet.

What is problematic about this is that it is arguing against a strawman, and is founded on amphiboly. The "species" or "kind essentialism" here is found in some philosophers, yes, from Locke to Mill, but not for biological species. In fact, nearly everyone who comments on this from Locke to post-Mill makes explicit exemption for biological species. Whately, Bentham, Mill himself, through to the masterful tome that was the last flourish of the tradition (pre-formal) logic, Introduction to Logic by H.W. B. Joseph in 1906 (2nd ed. 1916) makes this very clear. The use of the same word "species" for logical kinds and for biological kinds was at best a homonym.

Now there is a kind essentialism of biological species - it was something that was developed in the 1950s by analytic philosophers, and which was first explicitly assumed by Kripke and Putnam in the late 60s and early 70s. Philosophers of language have been debating this ever since. It is not, though, something that has ever informed natural history, or at least not before the Mendelians first tried to define species as "pure lines" in the 1910s. Whenever one assigns the date, though, it is well after, and in reaction to, evolution, rather than a view to which evolution is a resolution. The philosophical issues remain unaffected, but the dialectic is all wrong.

This, together with the fact that Linnaeus never actually defined the term species suggests that the entire history as devised by the Essentialism Story is flawed, and conclusions based on it are suspect. The polytypy of species was so well known that in 1928, based on a paper from two years earlier, a book entitled The Species Problem outlined it clearly. Intermediate forms, however, were well known problems as far back as the 16th century.

Summary: There never was an essentialist consensus,and fixity of species was founded on religious belief, not metaphysics or experience.