Me on Evolution Again

DNELSON at URIACC.URI.EDU DNELSON at URIACC.URI.EDU
Tue Aug 29 08:42:21 EST 1995


Just a couple of random thoughts on these exchanges that seem to pop up every
few months: 1) It is impossible for us to remove ourselves from selective/
evolutionary forces.  Even if one grows E. coli in LB at 37C, there will be
selection.  In the case of E. coli, the selection will be for fast growing
strains (If I recall correctly, this is the work of Kurland and his coworkers).

2) When we look at ourselves over a short timespan it is difficult to discern
which are the selective forces and which are just minor events which will have
little or no evolutionary impact.  Disease is one example: a one shot epidemic
may not have much evolutionary impact.  However, repeated and persistent
exposure to a debilitating and/or lethal disease could have an effect on
reproductive success.  An example - malaria is endemic in certain parts of the
world.  It is in those populations that certain mutations in hemoglobin have
been selected that result in less illness from malaria, but the price is
sickle cell anemia or other pathologies.  It has also been suggested that
some populations have greater resistance to tuberculosis due to prior
generations long-term exposure to this disease, but this has not been clearly
shown.

3) Since we have very slow gerneration times as opposed to bacteria, we will
certainly have more effect on bacterial (and viral) evolution than the
opposite.  By all accounts syphilis (aka the great pox) was a much more lethal
disease in the 15th and 16th century than today (even when not treated).  The
best guess is that Treponema pallidum evolved to be a much less virulent
pathogen.  Afterall, a pathogen that can live in it's host for many years
without killing it has a much better chance of getting passed to a new host
than a extremely  virulent pathogen like Ebola (Zaire).

4) The point is that evolution occurs no matter what.  You can often discern it
in bacteria (a point made by others here).  You might see it in moths or other
insects or other rapid generation plants and animals.  But no matter how hard
you try, it will be very difficult to see it happening to modern man.  We don't
have long enough life spans to see 50-100 generations.  We also don't have the
data base to look back and see it.

DAVID R. NELSON
DEPARTMENT OF BIOCHEMISTRY, MICROBIOLOGY, AND MOLECULAR GENETICS
UNIVERSITY OF RHODE ISLAND
KINGSTON, RI 02881
PHONE: (401)792-5902
FAX: (401)792-7148



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