The Development of the Philosophy of Species 307processes at the cellular, organ, and physiological level become important. In organ-
isms with behavioral signaling (that is, with nervous systems and sensory organs),
reproductive behaviors like calls and movements become important. Sex acts to
ensure that the organisms that can interbreed tend to be those whose genome and
anatomy are consistent enough. I call this reproductive reach: the more closely two
organisms are related, the more likely they are within each other’s reach as poten-
tial mates, and so the species is maintained by reproductive compatibility, and of
course some ecological adaptation. This is very similar to a definition of the gene-
ticist Alan Templeton, who said that species were “the most inclusive population
of individuals having the potential for phenotypic cohesion through intrinsic cohe-
sion mechanisms,” “that defines a species as the most inclusive group of organisms
having the potential for genetic and/or demographic exchangeability.”^69 “Genetic”
exchangeability here means the ability to act in the same manner in reproduction—
any two members of the species are (more or less) interchangeable. “Demographic”
exchangeability means that any two members of the species behave the same, eco-
logically, behaviorally, and so forth, and are interchangeable (more or less). With
these two causes of being a species, we can now narrow down the number of con-
cepts to two: ecospecies or biospecies.
There’s a philosophical matter to clear up. These causal explanations are just that:
explanations. They are not the concept of species. There was a concept of species
before we had any clear idea of what they might be. We identified species in the
fifteenth century that are still regarded as species, and there wasn’t the slightest
whiff of a theoretical biological explanation in the air at the time.^70 There is also a
difference between the use of species definitions as aids to discovery, and explana-
tion. A number of species conceptions have been formulated as operational aids to
identifying a new species. Some of these are genetic or molecular^71 and some are
morphological,^72 but many conceptions have attached to them species delimitation
techniques or protocols.^73 Mostly these are protocols of the sub-discipline or field
rather than natural classifications. Many of them are phenetic or phylogenetic con-
ceptions, or both.^74 Theory-based concepts presume the universal applicability of
that theory outside the groups on which it was formulated.^75 Discovery techniques
that are based upon explanatory concepts are hostage to empirical fortune.
And it is an old concept, too, although the first simply biological definition of
“species” waited until 1686 when John Ray defined it. Ray’s definition was based on
a simple observation: progeny resemble their parents. Species are those groups of
organisms that resemble their parents. Versions of it go back to the Greeks. As I have
argued, this presumes there is some power, a generative capacity, to make progeny
resemble parents, and it seems to rely upon seeds. I call this the generative concep-
tion of species, and it was not only the default view before Darwin, but Darwin
(^69) Tem plet on 1989.
(^70) Aristotelian accounts of generation notwithstanding.
(^71) Sites and Marshall 2003, Caron et al. 2004, Hanage et al. 2005, Staley 2006, Birky et al. 2010.
(^72) For example, John and Maggs 1997, Purvis 1997.
(^73) DeSalle, Egan and Siddall 2005, Knowles and Carstens 2007, Raxworthy et al. 2007, de Queiroz 2007.
(^74) Templeton 1989, Mallet 1995, 2000, Beltrán et al. 2002.
(^75) For example, Wu 2001a, 2001b.