Introduction to the Species Problem

Abstract

Species concepts, or more generally, the species problem, are among the most debated issues in biology. Answers to the questions of what a species is, in what ways species really exist (if in fact they do) and how species can not only be defined but also recognized and delimited, belong at least as much, and some of them rather more, to the realm of philosophy than to that of biology, but at the same time they are of utmost relevance to biologists. There may be biologists who think that philosophy is purely theoretical and perhaps even, at times, somewhat aloof, or in short, providing some underpinning for the big picture, but largely irrelevant to their daily work as scientists. That is not quite true, particularly when it comes to the issue of species. Philosophy of science is not just philosophy about science but also for science. Whether biologists can or should learn more from philosophers about species than vice versa I don't know, and perhaps it is not an interesting question anyway, but I think it is fair to say that it is more relevant from a practical point of view for biologists to get the philosophy right than for philosophers to get the biology right. If philosophers neglect the biology of species, their theoretical treatment of species might become hollow and detached from biological reality, but they are unlikely to suffer any practical consequences because biological species are first and foremost entities of biology. It is biologists who describe species, count them, use them as proxies for different biological phenomena and analyse their phylogenetic relationships. In that regard (and that one only), philosophy of species and biology are a bit like mathematics and engineering---engineers should know their mathematics, or else whatever they want to build won't work. Unlike failures in engineering, which are very obvious, the case with species and biology is, unfortunately, much more difficult: biologists may continue to use flawed or inconsistent notions of species without ever being aware of it, producing spurious results in, for instance, biodiversity assessments or ecological studies. These flawed applications of species notions in turn may then be the basis of flawed decisions in ``real life''---prioritization of habitats based on species richness or the conservation status of species taxa are just two obvious examples. There is probably hardly any other biological concept that is used so differently and inconsistently as that of species, with sometimes disquieting consequences that have largely gone unnoticed by many biologists.