Iartanner asked this on my request line post earlier:
What do you think is the biggest–i.e., most prevalent–misconception about evolution, and what makes it so common?
That’s an easy one. The most prevalent, biggest, and a total misconception about evolution is…
Evolution is only a theory.
I can’t count the number of times I’ve heard this used in arguments from internet forums, to public debates, to TV ‘news’ programs. I think it would not be a mistake to say that everyone who has discussed evolution has heard this statement and that every creationist of any flavor has used this statement.
I have never seen anyone say “gravitation is only a theory” or “germs are only a theory”. Yet, creationists the world over, seem to think that “it’s only a theory” is a good argument against evolution.
Evolution is not ONLY a theory. It is also a fact. Evolution as a fact has been observed in the laboratory and in the wild world. It has been observed at the level of genes and proteins and at the level of communities of organisms. We have observed minor changes (such as the folded ear in Scottish fold cats) to complete genus level changes in within a single generation in wheat (I hesitate to say this since I can’t find the paper right now, but it has happened). There are hundreds of cases of documented evolutionary changes.
However, evolution is ALSO a theory. A scientific theory is defined very differently from the more common use of the word. In the everyday vernacular “theory” is more closely related to “scientific hypothesis”. So, what is a scientific theory?
Theory: In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.
The contention that evolution should be taught as a “theory, not as a fact” confuses the common use of these words with the scientific use. In science, theories do not turn into facts through the accumulation of evidence. Rather, theories are the end points of science. They are understandings that develop from extensive observation, experimentation, and creative reflection. They incorporate a large body of scientific facts, laws, tested hypotheses, and logical inferences. In this sense, evolution is one of the strongest and most useful scientific theories we have. Science and Creationism: A View from the National Academy of Sciences, Second Edition (1999)
As the NAS says, a theory is a very well supported description of what is going on in the world. The theory of gravity, even though we don’t really know what causes gravity, is a very well supported and understood aspect of how the universe works. We can use the theory of gravity to fling men 255,000 miles to land on the moon. We can use the theory of gravity to build skyscrapers that are thousands of feet tall. We can use the theory of gravity to find new planets light years from Earth.
In this sense, evolution is a very, very powerful theory. It is used by tens of thousands of scientists and hundreds of thousands of people on a daily basis. Evolutionary theory is used to develop new products (much more quickly and with better specifications than human engineers). The theory is used to build better production schedules, produce better medicines, predict patterns in everything from fishing to farming.
So, in that sense, it is a theory and very useful one that has withstood the test of time, experiment, and every other competitor hypothesis.