Big Idea II: Evolution is a scientific theory, subject to testing and revision.

It is often easy for students and even teachers to dismiss the theory of evolution as “just a theory.” However, such a statement stems from a fundamental misunderstanding of the scientific process and the rank of scientific theories within it.

The term “theory” in everyday language means a mere guess or speculation. In scientific language, however, theories are the highest order of scientific explanation and are generally accepted to be true by the scientific community as a whole. A scientific theory is a synthesis of a large number of accepted and highly tested hypotheses. Scientists continue to test, refine, and add additional hypotheses to make a theory more concise, but it is highly unlikely that the whole theory will ever be replaced. In physics, a similarly supported theory is gravity; in chemistry, a good example is the atomic theory (that all matter is made up of particles called atoms).

There is no ongoing current debate among knowledgeable biologists about whether evolution occurs or has occurred. There is still vigorous debate about the details of how it occurs.

For more discussion on this topic, see the section Why Study Evolution?: Defining “Science.”