Re: Speciies? you gotta be kidding.
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You seem to be making the case that if we took a litter of puppies and totally isolated them into two groups on remote islands we have now created two species because they WILL diverge, drift, etc.
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I must be being unclear because this is certainly not what I'm saying. In this case they are interfertile and genes can flow between them.
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Yet, in fact, nothing has changed, we still have 'a group of puppies from the same litter.' Grabbing two groups from a ring species ( which we are all temporally a member of) is an upscale version of that.
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And I'm saying that it's not. The key to my point is that at some point two populations are unable to interbreed and no intermediaries exist to allow gene flow from one group to another. At this point, and not before, they are different species. They now will have a new class of different independent evolutionary trajectories that do not overlap (while there certainly may be convergence, etc. since they have a lot of the same raw materials).
These points are the joints.
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