
08-07-2011
Quote:
Originally Posted by Pertinax
Thankyou for this explanation (the Camels). I must admit to finding it hard to accept the concept of very similar looking animals actually being different species- such as for example the two White Rhinos- given their virtually identical appearance. I sometimes wonder how correct 'the science' really is in these things? Isn't it just more 'splitting' instead of 'lumping'? 
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'Science bit' warning!
The science of divergence as measured by DNA difference is very good. Using non-coding DNA regions you can get a 'molecular clock' as there is negligable selection on these regions so changes only happen by mutation - which happens at a predictable rate under normal conditions. As such, the degree of difference in these regions relates directly to the time since divergence.
As to whether this divergence makes them separate species, it's all to do with what species concept you're using. The traditional Biological Species Concept (i.e. two animal populations belong to the same species if they would produce fertile young if cross-mated) is less used these days, as there are too many cases where it simply doesn't seem to follow what's happening in all other measures of 'specieshood'. Many taxonomists would work from a genetic (based on species being a certain %age different) or phylogenetic (based on species being groups of individuals with a single common ancestor within a certain age range).
Wikipedia actually has a nice description of the differences between Biological and Phylogenetic species concepts, that explains why PSC tends to 'split' more than BSC:
"the difference between the BSC and the PSC can be summed up insofar as that the BSC defines a species as a consequence of manifest evolutionary history, while the PSC defines a species as a consequence of manifest evolutionary potential. Thus, a PSC species is "made" as soon as an evolutionary lineage has started to separate, while a BSC species starts to exist only when the lineage separation is complete. Accordingly, there can be considerable conflict between alternative classifications based upon the PSC versus BSC, as they differ completely in their treatment of taxa that would be considered subspecies under the latter model (e.g., the numerous subspecies of honey bees)."
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