First, we should clarify what "evolution " means. Like so many
other words, it has more than one meaning . Its strict
biological definition is "a change in allele frequencies over
time." By that definition, evolution is an indisputable fact.
Most people seem to associate the word "evolution" mainly with
common descent, the theory that all life arose from one common
ancestor. Many people believe that there is enough evidence to
call this a fact, too. However, common descent is still not the
theory of evolution, but just a fraction of it (and a part of
several quite different theories as well). The theory of
evolution not only says that life evolved, it also includes
mechanisms, like mutations , natural selection , and genetic
drift , which go a long way towards explaining how life evolved.
Calling the theory of evolution "only a theory" is, strictly
speaking, true, but the idea it tries to convey is completely
wrong. The argument rests on a confusion between what "theory"
means in informal usage and in a scien