By Roger Hull

Probably most of us have heard the phrase “It’s only a theory” applied to evolution. It’s usually used to indicate that while the Biblical creation story is “fact,” evolution is “only a theory.” Perhaps what is needed is to define three terms, fact, hypothesis, and theory.  

A fact is something known to exist or to have happened. For example, “I went to a concert last night and the lead singer was dressed all in black.” That’s a fact but it doesn’t tell me what the singer wore at his last concert or what he’ll wear at his next concert.  If I’m curious about whether he always wears black when performing, I need to form and test a hypothesis.

A hypothesis is a proposition set forth as an explanation for the occurrence of some specified phenomenon. In this case, my hypothesis is, “The singer always wears black when he appears in concert.”  To test this hypothesis, I must collect some data. I attend more concerts, talk to people who have attended concerts and review videos of concerts. After collecting this data suppose I find that in every instance, the singer wore black. I can now propose a theory.

A theory is a coherent group of general propositions used as principles of explanation for a class of phenomena; in this case, “The singer always wears black when he appears in concert.” A theory is useful because it is predictive (it can be used to predict what the singer will wear at future concerts). However, theories are subject to probability. In our case, there’s always a chance that the singer will wear something other than black at his next concert. So I must assign a probability to the theory, like the weather person does when predicting rain, for example. The probability depends on the amount of data I have collected. The more data I have, the greater the probability that that the theory will be predictive (that he’ll wear black at his next concert).

A theory is always subject to change. For example, suppose we find that the singer wears white when he performs in his hometown. We then must create and test a new hypothesis, remembering to apply a level of probability dependent on the amount of data we’ve collected. Our revised theory is, “The singer always wears black when he appears in concert except he wears white when he performs in his hometown.”

The theory of evolution is not as simple as our example, but the same criteria and method apply. For example, evolution could explain why mostly black bugs live on islands with black sand and mostly white bugs live on islands with white sand. It might be because birds can more easily spot white bugs on black sand so black bugs are more likely not to be eaten and will live to reproduce. Evolution has predictive value. For example, if we switched the color of sand to white on the mostly black bug island, we would predict that after several generations the bugs on that island would eventually be mostly white.

Today evolutionary theory is being used to predict the effects of global warming. For example, we know that coffee trees require a certain range of temperatures to survive and produce. As the Earth warms, we would predict that the coffee trees will have to be planted at higher and higher altitudes. In fact, this is what is actually happening.

Hopefully this will aid in understanding these three terms and in recognizing the value of evolutionary theory.

Roger Hull lives in China Grove.