Smallpox

[Barry M. OConnor]

At 6:18 AM 8/2/96, Thomas G. Lammers wrote:

>So I vote to do it in.  Eradicate it.  I see far more potential for evil
>uses of the last remaining cultures than benigh ones.  Granted, we can't
>see the future; maybe smallpox could someday be our salvation.  But as a
>wise man once said: "The race isn't *always* to the swift, nor the battle
>to the strong, but that's the way to bet your money."
>
At its most basic biological level, the smallpox debate boils down to the
issue of coevolution.  The body of theory in this area regarding
host-parasite associations developed by Anderson & May and others supports
the notion of an "arms-race" between host and parasite.  The simplest case,
exemplified by the smallpox virus-human system, involves only two parties,
the parasite evolving to best exploit the host and the host evolving to
minimize or eliminate the effects of the parasite.  If the latter causes
the extinction of the parasite, so be it (evolution has no ethics).  An
example of the latter comes from the psoroptid mites, best known to dog &
cat owners (pet ear mites) and livestock managers (itch mites, scab mites,
etc.).  The Psoroptidae are also very diverse on primates, with many highly
host-specific species.  I developed a cladogram, published a few years ago,
showing a high degree of congruence between the phylogeny of the
primate-associated Psoroptidae and the order Primates itself.  The only two
primate groups to lack psoroptid parasites are tarsiers and humans.  The
most parsimonious explanation for this absence is extinction.  I suspect in
the case of humans, the mites lost out when we lost the majority of our
fur.
        So in the case of smallpox, there has been an evolutionary
"arms-race" and we won.  Just because the mechanism leading to the
extinction of the parasite was cultural/technological and not genetic
doesn't change the outcome.  We evolved large brains and a pleiotropic
effect of that condition is that we can use technology to eliminate a
specific parasite.  I don't see the difference between that and our
ancestors having eliminated their psoroptid parasites.


Barry M. OConnor                phone: (313) 763-4354
Museum of Zoology               FAX: (313) 763-4080
University of Michigan          e-mail: bmoc at umich.edu
Ann Arbor, MI 48109-1079  USA