Science Theories in Practice:

As the evolution/creationism debate continues in the US, one argument that creationists repeatedly use is that evolution is just a theory, not something that is actually proven (Creationist arguments: http://www.talkorigins.org/faqs/faq-misconceptions.html).

Unfortunately, people who make this argument don’t understand evolution (topic for another post) or scientific theory (http://en.wikipedia.org/wiki/Theory#Scientific_theories).

First, what is a scientific theory?

A theory is a set of statements that explains a group of observations; usually the statements have been widely tested and accepted. (In physics, either the theory or observations can come first.)

However, a theory is not taken to be the gospel truth (Bible reference used intentionally). Scientists understand that theories are not necessarily the final answer to everything in the universe.

For example, in my experience, most candy that is blue tastes like blue raspberry (http://www.candywarehouse.com/colors/blue-candy/). Thus, my theory is that all blue candy will taste like blue raspberry (as it should).

Figure 1: Young woman about to eat what appears to be a tasty blue raspberry lollipop (based on my theory).

However, if I come across a blue M&M that is disgustingly chocolate flavored, then I need to revise my theory that all blue candies are flavored like blue raspberry. This new piece of data has proven that my theory is either incorrect or incomplete.

I can either get rid of my theory entirely or adjust it.

My new theory might be that most blue candies are blue raspberry (not all), or all good blue candies taste like blue raspberry, etc.

So, when a scientist says that a theory is true, this is short-hand for “this is the theory that makes the most sense of the data we have so far. If more data comes along that disproves this theory, then we will revise our theory.”

This subtext is what many non-scientists neglect: Theories can and must be altered if the data requires them to be changed.

A theory is not immutable, but instead our understanding of a theory can change in response to new data.

So if a person argues that evolution is just a theory, and it’s not proven, he or she has misunderstand scientific theory entirely (and proven how bad science education in this country can be).