2.2 Evolution Overview

What is evolution?

Simply stated, evolution is change over time. In biology, evolution is a change in the frequency of a trait within a population of organisms from one generation to the next. Traits are characteristics of individuals, like tail length or wing color. Sometimes it is possible to observe rapid evolutionary change. For example, we can detect when the percentage of gonorrhea bacteria that is resistant to a commonly prescribed antibiotic changes from 1% to 100% over a matter of days. The individual bacteria that are susceptible to the drug die, and the resistant bacteria multiply. Unfortunately, the antibiotic is now ineffective against this gonorrhea population and the patient’s infection will need to be treated with an alternative drug. Other evolutionary changes occur over much longer timespans, particularly in organisms with longer lifespans.

Is evolution a fact or a theory?

Evolution is both a fact and a theory. When a change in the frequency of a trait in a population can be observed, the observed change is evolution, and it is a fact. However, the mechanism by which the change occurred (such as gonorrhea’s increased resistance to an antibiotic) is open to scientific scrutiny. We can hypothesize that gonorrhea became resistant through one of a few different evolutionary mechanisms, and we can then test appropriate predictions. In over 150 years of scientific experimentation, the evolutionary mechanisms discussed below have done an excellent job meeting predictions and explaining how life forms change. In fact, the evidence in support of these evolutionary mechanisms is so overwhelming that we can consider evolution among the most robust of scientific theories.