by Whit Gibbons

May 23, 2010

Last week, one candidate in the Alabama Republican gubernatorial primary race accused another candidate of being in favor of teaching evolution in schools, as if that were a political spear through the heart. One newspaper article suggested that the political shield held up to deflect that spear was an assertion that the accusation is untrue. A spokesperson in the shield holder's office told me that the candidate considers "evolution to be the most dominant theory to explain the origin of life." Not, perhaps, a ringing endorsement of the need to teach evolution in school; better, however, than what some politicians are saying.

But as much fun as dissecting Alabama politics might be, this column is an attempt to explain to certain people (such as the spear thrower) what "evolution" means. The following is written for the nonbelievers.

Evolution in its simplest form explains how the natural world works through natural selection. The consequences of evolution are seen every day. Charles Darwin's ideas of natural selection, survival of the fittest, and evolution are elegant in their simplicity. Anyone interested in understanding the way the world works should consider the basic concepts of the process. The following example shows how evolution (change) in a lizard species could occur in a natural manner.

Natural selection operates because some individuals have a trait that makes them more likely to survive than others. In this example, a species of yellow lizards lives on an island. Their yellow body color is genetic, but a few individuals have genes that produce green individuals. Lizards that are dull green in color are rare, but they are the same species as the yellow lizards and interbreed with them. The lizards live peacefully in their tropical paradise until a type of lizard-eating hawk moves onto the island.

When flying over the thick, dark green vegetation of the island, hawks easily discern bright yellow lizards. If a green lizard and a yellow one are sitting side by side on a green bush when a hungry hawk flies overhead, the yellow lizard will stand out like a beacon. The green lizard will probably escape detection. Which lizard is more likely to become hawk fodder? Obviously, the yellow one.

Consequently the green genes are more likely to be the ones passed on to the next generation. As the natural process in which hawks select and remove the yellow lizards continues, proportionately more green genes are inherited than are yellow ones. Eventually, the hawks virtually eliminate the yellow lizards while green lizards become abundant. Thus, the island lizards have evolved--changed--to become a population of green lizards, with yellow ones being very rare. Basic evolution has prevailed.

Another example, which most pet owners are aware of, concerns flea collars. Anyone old enough to remember the advent of flea collars in the 1960s will tell you that they were a godsend for flea-ridden dogs and cats. You put the collar on the pet and the fleas were gone within days, if not hours. No fleas all summer or the rest of the year. But flea collars are no longer as prevalent as when they were introduced, and the explanation is a simple one: the fleas evolved.

The original insecticides in the collars that killed the fleas and did not harm the dog or cat were very effective, killing probably 99.9 percent of the fleas. But guess what. That means 0.1 percent of the fleas did not die. They were able to survive the chemical onslaught and produce offspring. Those offspring were genetically different, although only slightly so, from the fleas that were dying in droves. The survivors had genes that allowed them to tolerate the insecticides, and they passed those genes on to their progeny.

An adjustment in genetic makeup within a population or a species is the essence of evolutionary change. So, for example, whatever flea protection you are using now will probably be less effective in 10 years for the same reason flea collars are now obsolete: evolution.

It's such a simple concept even a schoolchild can understand it.

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