Re: Extinction Distinctions revisited

[John Alroy <jack@homebrew.uchicago.edu>]

        I just jumped into this list, so I have no comment on what  
appears to be a long-winded debate regarding the ethical or  
philosophical implicatns of the overkill hypothesis. However, I do  
want to put my two cents in about the overkill hypothesis itself. I  
just reviewed a paper sent to Paleobiology discussing the matter, and  
although I can't divulge any of the details (and they're besides the  
point), I was really struck with the fact that people continue to  
take the competing climate/gradual extinctions models seriously. This  
strikes me as totally crazy. I'll get right to the point: even if you  
stretch out the late Wisconsin extinction of 30-odd mammal genera in  
North America over a 10,000 year interval (20 - 10 kybp) - and there  
is excellent evidence it actually occurred in 2,000 years or less -  
you still are looking at an extinction event that is 100 times faster  
than normal, "background" rates of extinction for North American  
mammals!
        Even this is an underestimate because the event had almost no  
impact on small mammals, and large mammals represented a minority of  
mammalian diversity at the time. I have never seen any persuasive  
argument that a climate/vegetation change of any kind could cause a  
massive, rapid, extremely selective extinction of ANY group despite  
similar climate changes (deglaciations) having occurred over and over  
again during preceding intervals in the Pleistocene. Meanwhile,  
documented cases of humans wiping out large terrestrial vertebrate  
species are legion. I can't for the life of me understand why this  
debate has continued for the last 30 years despite what seems to me  
like completely conclusive evidence in support of a generalized  
version of the overkill hypothesis (the blitzkrieg hypothesis is  
another matter).
        Since this IS a dinosaur list, I'll add another two cents -  
some of you may be confused by recent, needless debate about whether  
the K-T boundaries were a "real" mass extinction, whether they  
happened very rapidly, whether the dinosaurs were involved, and  
whether the Chicxulub bolide was really responsible. All of these  
skeptical gradualistic arguments are simply hot air, and if you want  
a good review of the latest developments check out Richard Kerr's  
excellent review of the recent "Snowbird" meeting - it was in Science  
a few weeks ago. I'm sure a lot of you have already seen it, and  
there was a very telling exchange of letters debating Kerr's review  
in a still more recent issue of Science, which demonstrate a  
remarkable capability for doublethink on the part of certain  
gradualists.