I often observe that in discussions of evolution, both evolution skeptics and those who embrace neo-Darwinian evolution are prone to make one of two significant mistakes. Both stem from a failure to distinguish between microevolution and macroevolution.
The textbook for a genetics course I took at the University of Waterloo defined evolution as “changes in allele frequencies in a population over time.” An allele can be described as a variation of a particular gene. Defining evolution in this way can be misleading; it would be more accurate to call this variation. No new genes are required, just variation in existing genes or the loss of existing genetic information. This sort of variation is typically referred to as microevolution.
Microevolution (variation) takes place through genetic drift, natural selection, mutations, insertions/deletions, gene transfer, and chromosomal crossover, all of which produce countless observed variations in plant or animal populations throughout history. Examples include variations of the peppered moth, Gal�pagos finch beaks, new strains of flu viruses, antibiotic-resistant bacteria, and variations in stickleback armour. Each year, thousands of papers are published dealing with examples of microevolution/variation.
The mistake I often hear evolution skeptics make is to the effect that “evolution” is all rubbish, bunk, and false. They are often astonished to learn that variation (which they completely agree with) is defined as “evolution.” The solution is for evolution skeptics to be more precise on exactly what they have problems with. They can endorse microevolution (variation) but point out that a) it is misleading to call variation “evolution” and, b) their problems are with macroevolution.
The definition of macroevolution is surprisingly non-precise for a scientific discipline. Macroevolution can be defined as evolution above the species level, or evolution on a “grand scale,” or microevolution + 3.8 billion years. It has never been observed, but a theoretical example is the evolution from a chordate eel-like creature to a human being. Many people who embrace Darwinian evolution confidently state that evolution is a proven fact. They say this on the basis of thousands of papers discussing microevolution. Herein lies the second mistake … the assumption that because variation/microevolution is such an overwhelmingly proven fact that, therefore, macroevolution must be as well.
Macroevolution is very different from microevolution. The reason there are so many countless observations of variation/microevolution is that it requires no statistically significant levels of novel genetic information; it is trivially easy to achieve. The reason that macroevolution has never been observed is that it requires statistically significant levels of novel genetic information. It is extremely difficult to achieve, but Darwinian theory predicts that genetic information can significantly increase over time. Falsifiable predictions can be made and these are worth examining.
So in order to clearly distinguish between microevolution and macroevolution in a rigorous scientific way, let me propose the following definitions:
Microevolution: genetic variation that requires no statistically significant increase in functional information.
Macroevolution: genetic change that requires a statistically significant increase in functional information.
Both statistical significance and functional information are defined in the literature. We also have a method to measure evolutionary change in terms of functional information, so we are ready to move on, avoiding the two mistakes discussed above.
Photo credit: Kirk Durston.