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Evolution: Variation is the Theme
Marta L. Wayne, PhD, University of Florida
Presented for the Society for the Study of Evolution
at the "Teaching Evolution" Symposium: NABT Ft. Worth, 10/99

Evolution: Variation is the Theme
Marta L. Wayne, Ph.D.
University of Florida

When people think about evolution, they often think about natural selection - a major mechanism by which evolution works. However, the fundamental requirement for evolution is not natural selection, but genetic variation. Darwin emphasized how important it was that there were different varieties of a given trait, and that these varieties must be heritable, that is, genetic. From microevolution, e.g., the pepper moths that were selected for dark coloration during the pollution of the industrial revolution, to macroevolution, e.g., the creation of new species, genetic variation is key.

The advent of molecular biology caused a fundamental change in the way researchers think about evolution. Biologists were able to recognize that the heritable variation they were observing was caused by changes to the DNA. More importantly, it was even possible to figure out which changes in the DNA caused the changes in the organism that natural selection appeared to be recognizing. We can look at a collection of DNA sequences and see the footprints of evolution by natural selection. We can use this evidence to suggest which genes were important in evolution, even if the effects of these genes are unknown. And, we can use sequence comparisons to identify which change of many within a given gene is the change that evolution acted on.

In addition to understanding evolution at a level which has never been possible before, the study of evolution at the level of the DNA makes it possible for us to perform amazing feats in medicine, law, and agriculture. By understanding how selection acts on DNA, we can identify genes which cause disease. Recent examples of this include the breast cancer gene, BRCA1. We can also now recognize that multiple changes in a gene cause the same disease, and that the different changes are sometimes more common in some populations than others, because the evolutionary lineages of the populations are different from one another. This is important when we think about genetic testing: the fact that you donít have one particular mutation does not mean you are not a carrier for the disease by virtue of some other mutation in the same gene. And which mutation we are looking for will depend on which population the person is coming from. Thus genetic testing works well only when we keep evolution in mind.

Evolution is also essential for the equitable application of DNA forensics. Because different populations of people have different evolutionary histories, people from different geographic regions or different ethnic groups can have specific DNA characteristics present at different frequencies. It is these frequencies that are used to identify and convict criminals. For example, an expert on DNA forensics will explain that a given combination of DNA characteristics that was found at the scene of the crime is present in the population at large one in a hundred times vs. one in a billion times. If we use the wrong frequency, we could wrongly convict (or wrongly free) a suspect. Understanding evolution is the key to using the correct frequencies, and thus to doing justice.

Finally, we will soon be facing a worldwide food shortage. One approach to this problem is to try to breed plants with higher yields. Populations of plants, like populations of people, have different evolutionary histories. These histories influence how we can detect which genes will confer higher yield. We can also identify genes that cause plants to do better in certain environments, resist certain diseases, and so forth. Any endeavor that involves identifying genes involves understanding evolution.

Genetic variation is the ìstuffî of evolution. Further, the ways in which genetic variation is shaped by evolution provide a rich resource that is being used to benefit society in a wide variety of ways. The importance of evolution, particularly its genetic aspects, can hardly be overstated to our students.