On Tue, 10 Jun 1997 21:54:43 -0500, Glenn Morton wrote:
[...]
GM>I would not say that mutations have never been known to produce
>anything good for the organism which possess it. Over the past 60
>years, mankind has waged an unrelenting battle against the microbes
>of this planet. We have killed them with penicillin, streptomycin,
>vancomycin, and many other antibiotics. Because of this onslaught,
mutations have produced immunities to each of the antibiotics which
>we have thrown at them....
The impression here given (perhaps unintentionally) is that
favourable mutations arrive on demand when needed? My understanding
is that it is not "mutations" but genetic variation already present
in the populations that confers such resistance:
"...there can be no doubt that the staggering amount of genetic
variation in natural populations provides ample opportunities for
evolution to occur. Hence it is not surprising that whenever a new
environmental challenge materalizes-a change of climate, the
introduction of a new predator or competitor, man-made pollution -
populations are usually able to adapt to it. A dramatic recent
example of such adaptation is the evolution by insect species of
resistance to pesticides. The story is always the same: when a new
insecticide is introduced, a relatively small amount is enough to
achieve satisfactory control of the insect pest. Over a period of
time however, the concentration of the insecticide must be increased
until it becomes totally inefficient or economically impractical.
Insect resistance to a pesticide was first reported in 1947 for the
housefly (Musca domestica) with respect to DDT. Since then
resistance to one or more pesticides has been reported in at least
225 species of insects and other, arthropods. The genetic variants
required for resistance to the most diverse kinds of pesticides were
apparently present in every one of the populations exposed to these
man-made compounds." (Ayala F.J., "The Mechanisms of Evolution",
Scientific American, Vol. 239, No. 3, September 1978, pp56-57)
Although Ayala's example above is insect resistance to pesticides,
the context indicates he is speaking generally, and therefore I
assume he includes bacterial resistance to antibiotics.
God bless.
Steve
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