Douglas Futuyma, in his book Evolutionary Biology (1998), said, “Subspecies are quite arbitrarily defined; the same is true for genera, families, and other higher categories of classification. But one taxonomic category, the species, is thought by many to be real and non-arbitrary, and to play a critical role in evolution.” But what is a SPECIES? Ernst Mayr (1942) defined species as “a group of actually or potentially interbreeding populations, which are reproductively isolated from other such groups.” This definition has proliferated our (and I mean the Philippines) books, our classrooms, and I could be wrong, but could still very well be what your biology student, or teacher, will tell you. However, there is another definition, one that most of our students, or teachers, may not be familiar with. Joel Cracraft (1983) defined ‘phylogenetic species’ as “an irreducible cluster of organisms which is diagnosably distinct from other such clusters, and within which there is a parental pattern of ancestry and descent”.
Each definition is of course, not without criticism. Mayr’s Biological Species Concept begs the question: how can you define a species by simply basing it on reproductive capacity? What of fossils and asexual organisms? Are they not species as well? What of spatially-isolated populations? The differences in trait between two groups, even those not related to reproduction may not be sufficient to prevent them from interbreeding. This conundrum brings us to phenotype, which of course, also ushers in problems, given that phenotype is influenced by the environment.
The fundamental problem with Cracraft’s Phylogenetic Species Concept is that it requires a phylogenetic tree. But what if we cannot construct one for a certain organism? Is it not longer a species then? And what is ‘diagnosably distinct’ anyway? Who defines that? Who draws the line in such a hierarchical concept as the tree? And, how much weight do we give each of these: morphological, behavioral, or molecular diagnosibility?
So what if we do not have a clear definition of a species? Well, rightly, or wrongly (and this could be another blog!) our conservation activities are often centered on certain ‘species’. Our policies, action plans, management schemes, and the very core of our work rely heavily on ‘conservation status’, which is assessed mostly on the ‘species’ level. Enough said.
The debate amongst scientists is sizzling hot such that publications on the topic are spit out out like an old woman chewing on nganga. Join the kerfuffle?