Species concepts and philosophy

Note the use of the tedious-sounding word "concept" in this debate, which means we are getting bogged down in philosophy rather than doing science. Darwin himself had no time for philosophers, and he certainly didn’t like the philosopher's idea that species existed independently of human thought. Instead he argued that we humans must find a sensible and useful way to delimit actual species taxa. The idea that species are "real" and independent of human thought goes back to the Aristotelian essentialism that he needed to eradicate in order to show that species evolved. Under essentialism, species are defined by a kind of "essence" of speciesness; according to essentialists, we simply have to find out what this essence is. If it isn’t due to their being created separately, it must be something biological, reason the philosophers. But what?

Darwin rejected essentialism.  However, most modern species concepts search for a concept which underlies all species, and can be seen as a return to essentialism.  Many modern philosophers of science believe that scientific problems must be about "real entities", and they consider species as being "real".  If they are real, then there must be a fundamental basis or truth underlying all species.  The types of underlying truth include interbreeding within the species and lack of hybridization between species (as in the biological species concept), fundamental phylogenetic branching (as in some varieties of the phylogenetic species concept), or ecological role (as in the ecological species concept).