Little boxes on the hillside,
Little boxes made of ticky tacky,1
Little boxes on the hillside,
Little boxes all the same.
There’s a green one and a pink one
And a blue one and a yellow one,
And they’re all made out of ticky tacky
And they all look just the same.
When I taught invertebrate zoology at UNBC, I always started by going through classification systems, being careful to emphasize that classification is a purely human construct. In natural systems boundaries between closely related organisms may or may not be clear, and there is certainly no biologically functional reason for such boundaries. Each species can perhaps be viewed more like a continuum of genotypic and phenotypic characteristics, more or less clearly distinguishable from its closest relatives. The same is true for gender, where our dichotomous view of male and female doesn’t hold up even in many seemingly clear cases, e.g., human beings. A definition of species may work well for one taxon, but may be shaky for another. Even when it does appear to work well, there are always exceptions. For example, phenotypic variation of Lake Malawi cichlids (a flock of ~500 species radiated over the past 1-4 million years) would seem to show a large number of clearly definable species, but even morphologically disparate species can often produce viable and fertile hybrids under the right circumstances. A similar
radiation has occurred in Lake Tanganyika, albeit less massive. The ring species concept has been a problematic issue in some species definitions, but molecular studies has led to this evolutionary phenomenon being questioned by revealing that the distance between adjacent populations of supposed ring species are more distinct than previously assumed, with a clear break at some point along the ring.
Among invertebrates it can get extremely hairy, with extreme sexual dimorphism (e.g., in Strepsiptera) and polyphenism causing confusion. Polyphenism is when different phenotypes can be generated by a single genotype (Simpson et al. 2012). Polyphenism can be induced by various environmental influences, e.g., food, season etc. The point is that two morphologically different specimens may be the same species, which makes identification (and perhaps classification) a bit tricky.
The problem with the approach of compartmentalizing biological systems is perhaps best illustrated by the amount of disagreement evident among biologists themselves. Different people use different approaches to determine where the boundaries should be, with one group (splitters) tending to subdivide groups, whereas the other (lumpers) tend to combine groups. This happens regardless of the level, i.e., see this discussion. Nevertheless, it is the plasticity of organisms that enable evolution to proceed, and it is through classification that we learn more and more about how organisms are linked through evolution to each other. Mostly at a pace that is not perceptible except on a geologic time scale, but proceed it does.
If you are an entomologist, taxonomy and classification become critical to your work. It may be ok to talk about mammals or even birds without knowing scientific names, but with insects and most other invertebrates it would be impossible. One reason to classify organisms is that it makes it easier to communicate about them. For example, by using the Latin name of an organism I can make a biologist understand what type of organism I am talking about, even if he/she has never encountered the particular species. Without a common language that links to a description, we would be lost.
As humans we seem obsessed with putting things in boxes. You are labelled as Christian or muslim, democrat or republican, socialist or conservative, black or white, rich or poor, man or woman etc. (as I did above with splitters and lumpers, which are of course not fixed, consistent categories). We seem to always focus on differences, rather than similarities. We are, however, all human beings, and as such we have many more similarities than differences. Perhaps we were on the way to speciation prior to ships and planes, but in our current global community, reproductive isolation has gone out the window, so to speak. Prior to that, we simply have not been around long enough to diverge into multiple species, even though we diverged enough to speak different languages and even look different. The evolution of these differences came about through reproductive and social isolation. I grew up in northern Sweden, where dialects were more similar within river valleys than between them, even when the distances were as small as 30-40 km.
Thus we are one species – not morphologically identical, but certainly not different enough that we should need to hate or kill each other. From a biological standpoint we are completely reproductively compatible regardless of phenotypic differences. Unfortunately our obsession with compartmentalizing everything leads to artificial boundaries, which leads to misunderstanding, hate and (in the worst case scenario) war. Which is why John Lennon wrote “Imagine”.
Imagine there’s no countries
It isn’t hard to do
Nothing to kill or die for
And no religion, too
Imagine all the people
Living life in peace…
Sefc, K.M., A.C. Brown, and E.D. Clotfelter. 2014. Carotenoid-based coloration in cichlid fishes. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 173C: 42-51.
Simpson, S.J., G.A. Sword, and N. Lo. 2011. Polyphenism in Insects. Current Biology. 21: R738–R749.