kinman2 at YAHOO.COM
Thu Apr 15 23:06:01 CDT 2004
When I look out the window at a robin, there is no doubt in my mind that it is a real species, and that this robin is going to mate with another robin. Of course, many other cases aren't so clear cut. When speciation has not progressed to such a clear cut point (and more intermediate forms are still extant), it can get really tricky.
I believe that the vast majority of speciations are mother species giving rise to a daughter species, but this usually takes a very long time, and the incipient daughter "semispecies" can be absorbed back into the mother species given the right conditions. It is thus a judgment call whether full speciation has occurred, and even then species can still interbreed under unusual circumstances. When the incipient daughter "species" is separate from the mother species geographically it can be very difficult to tell whether it could potentially be absorbed back into the mother species. In the case of a circle of subspecies (adjacent subspecies interbreed, but subspecies at the ends of the closing circle do not), the mother species is held together only by the intervening populations which could eventually be extirpated (or not).
Therefore, I regard species as real, but often not yet very discrete. The boundaries can be fuzzy in both space and time in those cases that happen to be caught in the act of crossing from semispecies to full species. Speciation is rarely speedy (as can be with polyploidy). Therefore, whether to regard the daughter semispecies as a full species is a judgment call. I remember making such a judgment call on a couple of "species" of Artibeus in Mexico (separated geographically from a widespread species north of Mexico, and several years later bat specialists came to the same conclusion in a formal publication. One or both could eventually be raised back to species status given certain additional evidence, but I personally doubt it. They seem to be two disjunct subspecies that have not reached species status yet and probably never will (even if they do continue to survive human pressures), but it is just a judgment call. Luckily robins have no such extant populations that create such doubt, but the continuity of evolution is such that one should expect a certain percentage of species will not be so clear cut. It comes with the territory. I fondly remember our discussion of a hypothetical "species" of man potentially developing on Mars. It helps demonstrate just how difficult and relatively rare speciation really is (given how long it usually takes). I'm probably open more than one can of worms here, but what the heck.
--------- Ken Kinman
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