Imagine if a prominent mathematician published the results of his investigation of the value of the number "3", and demonstrated that our understanding of that number's value was actually wrong. Or if physicists proved that the length of time referred to as a "second" had to be increased by 4%. No matter how strong by the basis for these changes, they would raise a great deal of concern because of the effect they would have on everything else. Nothing may have changed about the actual state of things, but the way people describe that reality and their attitude towards it may need to be changed significantly. At some point the question is bound to be raised - should people change to using the new more accurate values, or should the old values be retained for the sake of stability?
This is the dilemma faced by taxonomy on a regular basis. On the one hand, taxonomy is a process of scientific investigation like any other, and our descriptions of things will inevitably change as our understanding of them improves. On the other hand, taxonomy does not exist as an end in itself, but provides as its results the basic units of communication for all other branches of biology. Recognising that what was thought to be two populations of a single species actually represent two completely separate species requires more than simply another entry in the checklist - it affects the way we deal with those populations. Do we need to revise their conservation priorities? When previous studies referred to the old collective species concept, which of the two species currently recognised was intended? Leme (2003) discussed the effects of changes in taxonomy on the conservation of Brazilian bromeliads, and highlighted the case of a 'rare' species of bromeliad that was suggested to be a synonym of another more widespread species. Should the rare taxon be maintained as a separate species because it would no longer be regarded as a conservation target if synonymised?
While change in concepts is almost always good when dealing with a scientific process, it does not automatically follow that it is advantageous when dealing with communication. Usually, it is - if the short-term disadvantages of losing old modes of communication are outweighed by the long-term advantages of adopting the new, then change remains the best option. The replacement of the telegraph by the telephone would have required a large investment of time and money, but the eventual outcome would have made it worth it. The dilemma is deciding when to make the investment.
A good example for taxonomy is the higher classification of birds. The most widely used system for classifying birds at present is the Wetmore system, established by Alexander Wetmore (the bloke in the photo above) in a series of publications between 1930 and 1960 (Wetmore, 1960). In the years since, continuing investigations into bird phylogeny have identified a number of inaccuracies in the Wetmore system (Hackett et al., 2008). Several of the taxa recognised by Wetmore, such as his 'Falconiformes' and 'Ciconiiformes', probably represent polyphyletic assemblages whose members have acquired similar adaptations to similar ecological niches rather than sharing an actual close evolutionary history. Despite the widespread recognition of these inaccuracies, many publications on birds such as field guides continue to use the Wetmore system. Why would they do so? Mainly because, as inaccurate as the Wetmore system may be, no strong competitor has yet taken its place. Even if the only reason for maintaining the status quo is simply that it is the status quo, most users are arguably better served by having a single widely-recognised system than a number of competing systems. Once a more accurate classification becomes more firmly established, a single wholesale change may be preferable to a series of cumulative changes. There may be other non-scientific factors involved too - even if storks and herons or grebes and divers are not actually each other's closest relatives, a certain appeal probably exists for field-guide authors in keeping these groups close together if they are the taxa most likely to be confused by bird-watchers.
In a recent post, I commented on the arguments for and against adoption of phylogenetic nomenclature, and ended up effectively arguing for a double standard. While adoption of phylogenetic nomenclature might be preferable from a theoretical basis, it may cause practical problems if researchers attempted to apply it to taxa whose phylogeny was not sufficiently well known. Similarly, in the bromeliad example referred to above, Leme (2003) recommended that even if doubts existed about the validity of an 'endangered' taxon, researchers should err on the side of maintaining its validity because otherwise they risked threatening its conservation status. From a theoretical perspective, Leme is completely wrong. Surely researchers should accept the result that their data indicates, whatever the practical consequences of that result might be? But from a more pragmatic point of view, is it responsible for researchers to ignore such consequences?
Ultimately, both these issues call for some sort of compromise. Change is a necessary consequence of improving knowledge, but change should arguably be instituted responsibly. Of course, no-one is going to ever agree about what counts as "responsible". That's the problem with compromise.
Hackett, S. J., R. T. Kimball, S. Reddy, R. C. K. Bowie, E. L. Braun, M. J. Braun, J. L. Chojnowski, W. A. Cox, K.-L. Han, J. Harshman, C. J. Huddleston, B. D. Marks, K. J. Miglia, W. S. Moore, F. H. Sheldon, D. W. Steadman, C. C. Witt & T. Yuri. 2008. A phylogenomic study of birds reveals their evolutionary history. Science 320: 1763-1768.
Leme, E. M. C. 2003. Nominal extinction and the taxonomist's responsibility: the example of Bromeliaceae in Brazil. Taxon 52 (2): 299-302.
Wetmore, A. 1960. A classification for the birds of the world. Smithsonian Misc. Coll. 139 (11): 1-37.