The debate over evolution can be confusing because equivocation has crept into the discussion. Some people use “evolution” to refer to something as simple as small changes in the sizes of bird beaks. Others use the same word to mean something much more far-reaching. Used one way, the term “evolution” isn’t controversial at all; used another way, it’s hotly debated. Used equivocally, “evolution” is too imprecise to be useful in a scientific discussion. Darwin’s theory is not a single idea. Instead, it is made up of several related ideas, each supported by specific arguments:
- Evolution #1: First, evolution can mean that the life forms we see today are different than the life forms that existed in the distant past. Evolution as “change over time” can also refer to minor changes in features of individual species—changes which take place over a short amount of time. Even skeptics of Darwin’s theory agree that this type of “change over time” takes place.
- Evolution #2: Some scientists associate the word “evolution” with the idea that all the organisms we see today are descended from a single common ancestor somewhere in the distant past. The claim became known as the Theory of Universal Common Descent. This theory paints a picture of the history of life on earth as a great branching tree.
- Evolution #3: Finally, some people use the term “evolution” to refer to a cause or mechanism of change, the biological process Darwin thought was responsible for this branching pattern. Darwin argued that natural selection had the power to produce fundamentally new forms of life. Together, the ideas of Universal Common Descent and natural selection form the core of Darwinian evolutionary theory. “Neo-Darwinian” evolution combines our knowledge of DNA and genetics to claim that mutations in DNA provide the variation upon which natural selection acts.
When you see the word evolution, you should ask yourself, “Which of the three definitions is being used?” Most critics of neo-Darwinism today focus on Evolution #2 or Evolution #3. But the discussion gets confusing when someone takes evidence for Evolution #1 and tries to make it look like it supports Evolution #2 or Evolution #3. Conversely, someone may discuss problems with Evolution #2 or Evolution #3, but is then falsely accused of rejecting Evolution #1, as well. This is simply not the case, for even biologists who dissent from neo-Darwinism accept Evolution #1.
For more information on this topic, read “The Meanings of Evolution” by Stephen Meyer and Michael Keas.