May 17, 2015

Blair Hodges
Carnell Professor and Director
Center for Biodiversity
Temple University
1925 N. 12th Street
Philadelphia, PA 19122

Dear Professor:
Your work was drawn to my attention by the site of hbd chick:
Her good humored approach to difficult matters, her charm and her incredible energy win the highest respect from me.  She has recently posted a link:
to an article:
in which you and a colleague constructed a vast evolutionary tree and calculated the time between speciation events for many life forms.  I have looked at their data, and it is most impressive.  You propose that speciation events occur most commonly at 2 million years with a lot of them tailing out to much longer times and propose that selection has nothing to do with it; it’s just a matter of random mutation.  I would agree with this latter, but that 2 million years seems rather long since my own best guess has been 2 thousand generations.  Accordingly I posted on the site a comment suggesting that I was confounded by the fact that the last common ancestors of chimps and humans was around some 6 million years ago.  3 steps from chimpanzee to human, indeed Homo sapiens, there having been other humans ancestral to us?  I don’t think so.  All right, the chimpanzees have changed as well, but that common ancestor was as different from them as it was from what we are now.  There are just too many differences.  The link describes the honeycreeper bird in which different species are marked only by a change in the shape of the bill (and whatever else the birds might be using to make sure they are mating within species). 

But the data are very persuasive.

I suspect that while I am talking about allopatric speciation, speciation in which two populations are strictly isolated, in fact there is something called sympatric speciation in which there is no such isolation.  And since most animals spend most of their lives in populations that have not been divided by glaciers, coastline changes or whatever, it seems reasonable to guess that the data you offer reflect sympatric speciation, the allopatric having been drowned in the statistics. 

And I think it reasonable to suppose that allopatric speciation is faster.  So although I regard the 2 million year evidence as a challenge to my own thesis (that fertility requires mating with kin within a few generations – see I do not regard it as a game changer.


M. Linton Herbert MD

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