The word theory, in the context of science, does not imply
uncertainty. It means "a coherent group of general propositions used
as principles of explanation for a class of phenomena" (Barnhart
1948). In the case of the theory of evolution, the following are some
of the phenomena involved. All are facts:
Life appeared on earth more than two billion years ago;
Life forms have changed and diversified over life's history;
Species are related via common descent from one or a few common
ancestors;
Natural selection is a significant factor affecting how species
change.
Many other facts are explained by the theory of evolution as well.
The theory of evolution has proved itself in practice. It has useful
applications in epidemiology, pest control, drug discovery, and other
areas (Bull and Wichman 2001; Eisen and Wu 2002; Searls 2003).
Besides the theory, there is the fact of evolution, the observation
that life has changed greatly over time. The fact of evolution was
recognized even before Darwin's theory. The theory of evolution
explains the fact.
If "only a theory" were a real objection, creationists would also be
issuing disclaimers complaining about the theory of gravity, atomic
theory, the germ theory of disease, and the theory of limits (on which
calculus is based). The theory of evolution is no less valid than any
of these. Even the theory of gravity still receives serious challenges
(Milgrom 2002). Yet the phenomenon of gravity, like evolution, is
still a fact.
Creationism is neither theory nor fact; it is, at best, only an
opinion. Since it explains nothing, it is scientifically useless.
Barnhart, Clarence L., ed. 1948. The American College Dictionary,
New York: Random House.
Bull, J. J. and H. A. Wichman. 2001. Applied evolution. Annual
Review of Ecology and Systematics 32: 183-217.
Eisen, J. A. and M. Wu. 2002. Phylogenetic analysis and gene
functional predictions: Phylogenomics in action. Theoretical
Population Biology 61: 481-487.
Milgrom, Mordehai. 2002. Does dark matter really exist? Scientific
American 287(2) (Aug.): 42-52.
