Paul pointed out that most mutations are harmful or fatal. However, the
probability of a beneficial mutation is by no means zero; it's just very
small. So if you're dealing with a very large population, especially one
that breeds very quickly and in large numbers, you should expect to see
beneficial mutations happening practically before your eyes. The most
extreme example known is HIV. The HIV particles in a single human body must
number in the trillions, reproduction is very rapid, and overturn of the
population is also rapid. The result is that HIV adapts to conditions
within each person it infects!
 
Bacteria are also good examples. By now, most everyone has heard of
bacteria that have become resistant to penicillin. The wee beastie that
causes tuberculosis seems to be particularly good at adapting to
antibiotics. And we've all heard of insects that can no longer be
controlled by DDT or other pesticides.
 
I am not suggesting that these are new species, but they are great examples
of beneficial mutation. In the case of animals that breed more slowly, or
that have smaller populations, of course we see a lot of pathological
mutations and hardly ever see a good one, though I think that one of the
academics on the list could probably provide examples. But, given millions
of years, millions of generations occur and that evidently is enough for
beneficial changes to accumulate even in slowly reproducing organisms.
 
Stephen Jay Gould pointed out a possible example in his book, "The Panda's
Thumb". The mutation that gave the panda a thumb-like finger (actually the
finger opposite the true thumb) was apparently a single, sudden one, and
the offspring would have looked crippled if anyone had been there to
witness. But this "thumb" allowed the panda to grasp bamboo and eat it. In
other words, it allowed pandas to be pandas instead of just another
bear-like omnivore.
 
Paul, I'm curious about these "freak" specimens of yours. Are they really
common? Do more of them show up in polluted environments--or in any
particular kind of setting, for that matter? Are they more common in dense
or sparse populations, if you have equal numbers of each?
 
Andrew K. Rindsberg
Geological Survey of Alabama