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Re: Extinction scenarios



In a message dated 8/19/98 2:20:32 PM Eastern Daylight Time, TomHopp@aol.com
writes:

<< When a plague strikes (bubonic, black, smallpox, etc.) even in an
 immunologically naive population, there are always individuals who
 "miraculously" are untouched.  These individuals just happened to have a
 histocompatibility allele that was resistent to the organism, and would
 repopulate in a geological instant, and MOST of their progeny would be
 resistant to the formerly "new" microbe. >>

I certainly don't contest Tom's superior biological expertise in this area.
But as someone with some background in Anthropology, I will note that viral
pandemics have been identified as _stong_ and _ contributing_ factors to
massive populations declines of Paleo-Indian populations in the North America
in the 16th and 17th centuries.  Perhaps those diseases would not, by
themselves, have delivered a death blow to those cultures, but by eliminating
a substantial percentage of the population they certainly dramatically
increased their susceptibility to outside influences that they may otherwise
have been able to resist. 

The corollary here is that some type of pandemic disease among the Dinosaurs
may have left survivors, for the reasons Tom articulates, but they would have
been few and far between.  Pandemic disease would have left individual
survivors who may have been able to sustain the population in normal times,
but in extraordinary times--such as those that witness a huge bolide
impact--those populations may not have been vigorous or numerous enough to
survive.

So here's a question for George: In the scenario sketched in the above
paragraph, is it the disease or the bolide that "caused" the extinction?