Morphological Species Concept - Biology As Poetry

A species concept is a way of defining or at least thinking about the differences between two species, especially otherwise quite similar species, and the Morphological Species Concept involves thinking about these differences in terms of how species differ in the shapes of their bodies and otherwise what they look like (including on the inside).

The morphological species concept is applicable particularly to situations in which the potential for mating along with postzygotic barriers to reproduction – which together define the biological species concept – cannot easily be determined. In practice, this is applicable to a great many situations since getting two organisms to prove to you, beyond a reasonable doubt, that they are unable to mate is not necessarily a trivial process.

This difficulty of assessing potential to mate increases infinitely if the two organisms in fact are dead, which is the case for organisms that are known only from the fossil record (i.e., which are fossils). A standard, indeed default approach by which organisms are distinguished into separate species thus involves characterizing organisms phenotypically, looking for consistent differences.

Such differences too are not necessarily easily determined and hence distinguishing among especially very similar species can require a great deal of knowledge and experience as well as attention to detail. Indeed, how much difference is sufficient to distinguish organisms into separate species ultimately can be function of opinion or personal temperament, i.e., contrast lumpers and splitters.

The morphological species concept is called "morphological" because the idea is based less upon molecular- or sequence-based approaches to systematics than one might expect from a modern perspective. Nevertheless, once upon a time organisms were distinguished primarily in terms of their morphology.

The study of phenotype has since been undertaken on more molecular scales and, indeed, distinguishing among organisms consequently has become very much sequence based. Since genotype at best only arguably might be included among morphological information, I limit the above definition to phenotype (top of page), which is broader than the idea of morphology sensu stricto but retains utility by not possessing infinite breadth. Differences in genotype nevertheless represent a key means by which different but otherwise similar organisms, today, are distinguished from one another. See also the pluralistic species concept.