A brief search failed to turn up the article referred to by George and I have not yet read the APS thread mentioned. When I have time I shall do so. In the meantime it seems appropriate to provide some clear background that will facilitate a clearer understanding of the system we have today and wherein the problems lie...
Theophrastus (370-285 BC), a student of Aristotle, was the first recorded attempted to name all pants, beyond just those of importance to humans. The Greek influence led to the use of Latin names, Latin being the common language via which philosophers and other academics communicated.
It was not until the seventeenth century that people in Europe took up trying to name all organisms once again. The Latin based utilised by the Greeks were utilised as a starting point. Names used by the Greeks were based on a description of the plant’s characteristics. To differentiate a new closely related species, distinguishing adjectives were added to an existing name. This system led to some very unwieldy names. For example, the common carnation was known as “dianthus floribus solitaris, squamis calycinis subovatis brevissimis, corollis crenatis”. This means “the pink (a general name for the group),with solitary flowers, the scales of the calyx somewhat egg-shaped and very short, the petals scalloped. By the eighteenth century using this descriptive based system of naming, many names become too long and difficult to use.
Carl Linnaeus (aka Carl von Linne) was responsible for instigating two revolutionary changes (that we still use today) to the way in which organisms were named. Firstly, he introduced the idea of a nested hierarchical structure, based upon observable characteristics that are shared, and that reflect natural relationships. The Linnaean system classified nature starting with three kingdoms. Kingdoms were divided into classes which were, in turn, divided into orders, and thence into genera, which were divided into species. The second idea he introduced was to name living things using a similar system to the way Europeans named people, except doing it ‘surname’ first. This binomial naming system has a couple of rules regarding the allocation of names. The genus name (and all names further up in the hierarchy must all be unique i.e. once used on particular group they cannot be used for any other group of living things. Species names may only be used once in any given genus but there is no restriction on the number of genera in which it may be used.
Up until Darwin and Wallace, the prevailing religious doctrine was creationism in which it was believed that the Creator made each form of living thing separately. At the same time the earth and its climate were believed to be immutable i.e. the same as the ‘day’ they were created. So the only real problem anticipated with classifying a new species of living thing (based upon its observable physical attributes) was ensuring that it had not been classified already.
Darwin, Wallace and Mendel, and those who have followed in their footsteps, threw a very large spanner in the works by determining that new species arise from pre-existing species through genetic change. Palaeontology and geomorphology have corroborated the notion of major changes to the physical and life structures of the earth.
There are a number of ways in which speciation (development of new species) can occur. One is breeding isolation. This normal occurs as a result of some form of geographical barrier that divides what was a freely breeding population, such a river changes course and creates an impassable valley, a mountain range, a wide body of water etc. Changes in behaviour, colour and/pattern and pheromones can also result in breeding isolation. Adaptive radiation is major driving force in speciation. As population spreads out geographically, sections of it adapt to the many varied ecological niches present. The proliferation of insect species in general and beetle species in particular is a prime example of adaptive radiation. Ctenotus and Lerista skinks are examples in Australian reptiles.
Genetic isolation does not have to be absolute. If the rate of gene flow between two populations is sufficiently reduced, these populations can develop along sufficient different lines to the point where separate species can develop. For example, there is a frog in the US that has a Ì-shape across the country. There 5 recognised populations A, B, C, D and E. Adjoining populations can breed readily as can two populations either side of another. However, Populations A and E are unable to produce viable offspring, despite the fact that these two populations occupy the most similar habitat.
So what are the issues confronting classification today?
Evolution is the development of a new species from pre-existing species. Because evolution is an on-going process,
While there are plenty of “end points” present as the result of evolution there also a lot of “still in the process”. While we might like to envisage evolution as a clear, one-way direction, this is not the reality. Evolution is a product of the environment and subject to changes as the environment changes. It is influenced by the unpredictable occurrence of mutations, random genetic drift and a few other factors, depending. Evolutionary influences will vary through time and with geographic location. As a result, different populations can exhibit specific genetic markers unique to them. At the same, the division between two genetically distinct populations may be cline (genetic change with distance) rather than a distinct separation as the result of breeding isolation (for whatever reason).
While the current classification system presents difficulties with certain groups and the taxonomists’ term of ‘’species complex” does nothing in real terms to help, the usefulness of the system cannot be over stated.
So while it may be a case of arbitrarily choosing a point of division, like choosing where red ends and orange begins on the visible spectrum, this does invalidate the immense value of a system of categorising living thing. Simply because one colour grades into the next does not make the colour classification scheme of ROYGBIV any less useful.
Blue
PS Sorry abut the length but I don't know how to put in more than one post at a time.
