In the philosophy of biology it has been claimed many times that a popular position regarding the question of what species are, among biologists, is cladism. For my current purposes, the defining trait of cladism is captured in the following quote:

According to cladism, a species becomes extinct whenever it sends forth a new side species. (LaPorte 2004, 54)

So, for example, if Homo floresiensis is truly a species, and it derives, via a speciation event, from Homo sapiens, then, after the speciation, there is no Homo sapiens: there is Homo floresiensis and a new species, very similar to sapiens. In general, whenever there is speciation the mother species disappears.

I am under the impression that this description of the situation is not the one most mainstream biologists would endorse. I take it that a more common description would be one under which, if a number of Homo sapiens get isolated in an island and go on to form a new species, Homo sapiens exists both before and after this speciation event. I would like to know whether cladism, described as above, is really a popular position, or whether I am right about what most biologists would say about the relation between floresiensis and sapiens.

It might also be that biologists declare themselves cladists when explicitly theorizing about the nature of species, but fall back to a less extreme form of cladism in the actual practice. Evidence in favour of or against this possibility (coming from biology, not the philosophy of biology) would also be appreciated.

As Noah has pointed below, what I have called extreme cladism might be very far from cladism, as usually interpreted. This is precisely the kind of claim I would like to see substantiated.

LaPorte, Joseph. 2004. Natural Kinds and Conceptual Change. Cambridge University Press.

  • $\begingroup$ Sorry, the following comments got toasted in a testing catastrophe - my fault: "Depending on how strong the emphasis is on monophyletic concepts, it would have the consequence that has been pointed in the question: if the "mono" in "monophyletic" indicates a single, non-branching stretch in the evolutionary tree, a species cannot survive its "sending forth a new side species", as LaPorte puts it." & ... $\endgroup$ – Rory M Jun 18 '12 at 21:34
  • $\begingroup$ "that seems to me to be very far from the defining characteristic of cladism. Instead I'd says cladism is characterized by emphasizing monophyletic concepts (archosaur or ray-finned fish) over polyphyletic ones (like reptile or fish) and emphasizing the arbitrariness of Linnaean ranks (calling everything a clade instead of phylum/class/etc.)." - many apologies :/ $\endgroup$ – Rory M Jun 18 '12 at 21:35

I've never heard of it, actually - though I can't speak for my professors or researchers I know, none have ever presented the Cladism argument as an argument for the delineation of species.

As far as I'm aware, the attempts to define a species fall along three lines:

The ability to produce fertile offspring in the wild.

Distinct physical characteristics.

An arbitrary amount of genetic divergence.


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