Darwin and Deleuze: species in motion

How does the temporality of evolution work? And if species are evolving, how is there such a thing as "species" anyway--why not a total flux? Darwin is clear that "species" is not a precise term. The difference between a "species" and a "variety" or subspecies is murky because species arise from varieties.

"Certainly no clear line of demarcation has as yet been drawn between species and sub-species.... These differences blend into each other in an insensible series; and a series impresses the mind with the idea of an actual passage" (The Annotated Origin 51).

Actual exemplar organisms can only constitute a series with discrete differences, but somehow these series amount to differences of species, for we see quite clearly that sheep are not pigs are not cows. But in another sense, one which Darwin must affirm, sheep are pigs differentiated only by temporal duration and environmental transaction.

(Incidentally, the text I'm using is this really beautifully done facsimile of the first edition of the Origin. Worth the 25-35 bucks if you can afford it).

This paradox sheds light on the metaphysical subtlety underwriting Darwin's new concept of evolution. The extant alternatives of Paley and Lamarck both wrangled with the difficulty of change in metaphysically conservative ways--both essentially see change as a surface phenomenon, Paley by punting processual agency to the deity (if it exists at all), Lamarck by tethering change to individual intention. (Darwin, on the other hand, upholds "unconscious selection"--the selection process might be concealed to all intentional actors.) Most importantly, change is not an extra metaphysical layer, the proverbial icing on the cake, but existence itself. Species exist as temporal accumulations. A being is a discrete organism and a point in a series of discrete organisms, but it is also and necessarily a blur of motion in a dimension of being that does see the series, a dimension better termed becoming; thus a being is "an actual passage." Darwin's fundamental, if unstated, metaphysical revolution then opens a whole new and profitably analytic despite the evidentiary gaps and downright errors in the Origin. (Remember he did not have Mendelian genetics at hand--can you imagine affirming Darwinism without a gene theory of inheritance?!)

The metaphysics of Darwinian evolution are put forward more concisely by Deleuze in a lecture on Spinoza:

"The affection envelops an affect...It is not a comparison of the mind in two states, it is a passage or transition enveloped by the affection, by every affection. Every instantaneous affection envelops a passage or transition. Transition, to what? Passage, to what?... There is a specificity of the transition, and it is precisely this that we call duration and that Spinoza calls duration. Duration is the lived passage, the lived transition." (From the Deleuze's lectures transcripts on Spinoza's affect)

The Origin of Species touts not just a theory for how species arose, but a radical redefinition of the concept "species" of which it is equally originary.