evolution-1: The common biological ancestry of all life on earth from
a small number (probably one) of ancestral forms. This is commonly
called the "fact of evolution." While, like anything else in science,
it is not "proven," it is established to the point where no rational,
unbiased scientist would refuse to accept it.
(This places it in the same standing as, say, a heliocentric
solar system. There are still "scientists" who accept a geocentric
solar system, but not because that is where the evidence leads them.
It is because their religious beliefs require it to be that way.)
evolution-2: (One example) The process of random variation coupled
with natural selection, which is theorized to have been a major
mechanism for evolution-1. When scientists talk about a "theory of
evolution," they are talking about a proposed mechanism by which
evolution-1 could have occured (there are several accepted mechanisms;
most of the arguments are over their relative importance for "large"
This treatment is simplified: A "theory" is an explanation for (and
predictor of) data which has already been quite successful when put
to the test (e.g., the "theory" of gravitation, electricity, atoms).
As "explanations for data" go, a "theory" is the top of the line.
A common creationist argument that evolution is "only a theory" is
like saying that your car is "only a Rolls Royce." (That argument
is also false, as described near the top of this article.)
Finally, if you look in _Science and Creationism_ (Ashley Montagu, Ed.),
Dr. Cuffey's essay lists technical references for more than a hundred
transitional forms at all taxonomic levels. We also have, in talk.origins,
several FAQs which deal with particular transitions as documented in the