Bryan reminded us that:
>The 1995 Official Statement on Teaching Evolution stated: "The
diversity of life [all life] on earth is the outcome of evolution: an
unsupervised, impersonal, unpredictable and natural process of temporal
descent with genetic modification that is affected by natural selection,
chance, historical contingencies and changing environments."
However, in the textbook Biology, by Miller and Levine,
(Prentice-Hall, 1993-2000 editions), the authors write "evolution is
without plan or purpose" and "evolution is random and
undirected" (p. 658).
Like Bryan, I'm fairly new to the discussion group; and I admit that I
was not intimately involved in the textbook wording debates of the last
couple of years; so please excuse me if what I'm about to say has been
said by others. I know that Van Till et al. made these points in
_Science Held Hostage_ and Bube made them in _Putting It All
Together_. It never hurts to be reminded...
I believe there is a context in which the above terms and statements are
appropriate in textbooks and definitions of evolution.
First, beginning biology students often have the mistaken notion that
evolutionary change (e.g., adaptation - even on an uncontroversial
microevolutionary scale) occurs because the organisms (actually, the
populations) somehow plan where they want to go. It is important to
correct this notion. The things that are evolving do not plan or
direct where they are going evolutionarily; they have no forward-looking
purpose of their own making.
Second, there is considerable evidence that mutation is random with
respect to phenotype. For example, the observed rate of
substitution among the four nucleotide states accords with that predicted
by known physical constraints on their probability. To date, all
complex distributions of genetic variation that seem puzzling on the
surface have later been found to be consistent with random mutation x
selection, drift, etc. At nucleotide positions that are known to
have no effect on fitness, the distribution of variation within and among
populations and species is random (i.e., probabilistic within known
physical constraints). There is much more that could be said in
support of this point, so don't think that by cursorily dismissing this
one example you will refute the point as a whole.
Perhaps the terms "chance", "random",
"undirected", "plan" and "purpose" are not
ideal because they pave the way for confusion (and misguided assertions
by atheists), but they are appropriate when confined to the domain of
science.
Doug
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