[Taxacom] An improved definition of cladogenesis

[Bob Mesibov]

You might also agree then with O'Hara that the 'species problem' is something we need to get over, rather than solve. We can simply see the living world as a tree of evolutionary relationships and we can stop trying to fit a classification on top of this.

This is the view of Joe Felsenstein, who in his 2004 book 'Inferring Phylogenies' has a section titled 'The irrelevance of classification': 'The delimitation of higher taxa is no longer a major task of systematics, as the availability of estimates of the phylogeny removes the need to use these classifications.' Referring to three conflicting views of classification - evolutionary-systematic, phylogenetic and phenetic - he announces a 4th school, 'It-Doesn't-Matter-Very-Much', and says that 'systematists "voted with their feet" to establish this school, long before I announced its existence'.

I personally don't think it's that simple. Unless you're prepared to place every single living individual on a tree, you need to define categories and say 'This group of individuals, only one of which I've placed in a phylogeny, are more or less equivalent for study purposes, conservation, etc'. I think most Taxacomers would agree that these categories are sort of ready-made in Nature, and we name them as species. Having got those categories, we now notice that our 'species' are likewise naturally grouped into categories we can call subgenera and genera, and so it goes, and before long we have a classification.

There's a more or less amiable relationship (in my mind, at least) between these two views of diversity, one looking like a tree and based on inferred relationships, and one looking like a hierarchical list and based on character state differences. Where I think we come unstuck is when we try to say that the two are the same, and start asking questions like: 'When does a species first appear?' Maybe the correct answer isn't 'You can't decide except in retrospect' but 'The question is meaningless.'
-- 
Dr Robert Mesibov
Honorary Research Associate
Queen Victoria Museum and Art Gallery, and
School of Zoology, University of Tasmania
Home contact: PO Box 101, Penguin, Tasmania, Australia 7316
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