Metaphysical Reflections on Biological Taxonomy

It has been said that taxonomy is dead, and yet there is much about biological systematics that is simply taken for granted. The present regime in biological taxonomy (at least for more complex forms of life) is to arrange living creatures in accordance with the best information available regarding their natural history (the so-called “tree of life”). Taxonomic decisions are typically informed by traditional comparative anatomy, as well as behavioural and population studies, but with increasing deference toward biochemical analyses, and in particular the results DNA hybridization experiments. The assumption underlying this approach is that affinities between biological organisms are best adjudicated and understood according to the degree of relatedness, or the most recent common ancestral organism (either postulated or for which a candidate is known). Contemporary taxonomy does not corroborate evolutionary theory so much as it exists in order to enshrine it.

Phylogeny is one very revealing perspective on the organization of life; where you come from says a lot about where you presently are. However it is a retrospective view of life, and historical relationships sometimes distort present relationships and the relative significance of the two. To cite an avian example, there is something counterintuitive and potentially counterproductive about grouping flamingos and grebes together more closely than, say, grebes and other swimming/diving birds (see Hackett SJ et al. 2008. A Phylogenomic Study of Birds Reveals Their Evolutionary History. Science 320: 1763-1768).

An alternative taxonomy (in some ways a more traditional taxonomy) might promote present ecological similarities between organisms with indifference to genealogical relationships. Such a taxonomy would centre around ecology as its organizing principle (rather than anatomy or phylogeny). This approach would have certain advantages over current taxonomic practice, for instance it would be more intuitive, and would focus more on current features and functions of an ecosystem, rather than historical affinities amongst extant taxa.

The point of these comments is not to challenge the status quo. The point is simply to observe that decisions regarding taxonomy, and the organizational principles behind them, depend largely on conventions which taxonomists stipulate in advance of their empirical investigations. These conventions in turn depend on the biases and predilections of taxonomists as well as their values and objectives. The first principles of the science of biological taxonomy are not themselves scientific, but rather they are metaphysical. It is worthwhile to reflect on these things from time to time.