Robert M. Pringle: Keeping science in debate over evolution

Robert M. Pringle: Keeping science in debate over evolution
By Robert M. Pringle and Paul R. Ehrlich - Sacremento Bee, 6/24/07
The 82nd anniversary of the Scopes "Monkey" trial occurs in July, and still evolution simmers on the national political scene. Debates on teaching evolution rage from California's Central Valley to the Carolinas, with many legislators and school boards advocating neo-creationism packaged as "intelligent design."

The subject has even made waves in the 2008 presidential race. Witness the Republican debate on May 3, when the question "Is there anybody on the stage that does not believe in evolution?" prompted U.S. Sen. Sam Brownback of Kansas, former Arkansas Gov. Mike Huckabee and Colorado Rep. Tom Tancredo to raise their hands.

These candidates have scrambled to explain their denials. In so doing, they have highlighted a rift that not only separates scientists from evangelicals but also divides the public: a Gallup poll of 1,007 adults June 1-3 indicated that 53 percent of Americans believe that humans evolved over millions of years, while 66 percent believe in divine creation in the past 10,000 years. These figures add up to 119 percent, suggesting that Americans are profoundly ambivalent.

Such confusion about evolutionary theory jeopardizes the health of our nation, and Brownback's waffling typifies how GOP politicians obfuscate the issue.

In an article following the debate, Brownback wrote, "If belief in evolution means simply assenting to microevolution, small changes over time within a species, I am happy to say, as I have in the past, that I believe it to be true."

The obvious corollary is that he does not accept macroevolution leading to the formation of new species.

This stance undergirds most anti-evolution arguments.

Since microevolution cannot be denied (it is observable in nature), politicians attempt to distinguish between that process and speciation, which produces new species over many human life spans. But we must scrutinize this distinction. It is deceitful, it is harmful and it only flies because Americans remain unfamiliar with evolutionary science and its methods.

Let's be clear: The evidence for the evolutionary origin of species is every bit as strong as that for microevolutionary processes.

Occasionally, speciation is dramatic, as when new species arise instantaneously by hybridization between existing species. More common, though, is gradual geographic speciation. Populations of a single species living in different areas are subject to different evolutionary forces. They gradually diverge until they become two or more daughters of the original species.

The ingredients in this recipe are environmental variation, genetic variation and time -- no hand of God is required. Every stage of this process has been documented repeatedly as scientists have explored the patterns of geographic variation within species and described the emergence of new ones.

Moreover, because scientists know the rates at which certain genes change, they can often estimate when in the past species split apart.

If two cars started in the same place and traveled in different directions at a constant speed, you can calculate when they left their common starting point. Similar calculations can be made for genes changing at approximately constant rates. Biologists use these methods to reconstruct evolutionary history, including that of our own primate lineage.

For example, recent estimates suggest that the human lineage diverged from the chimpanzee lineage 6-7 million years ago, and that humans and Neanderthals split around a half-million years ago.

Brownback's argument rests on the fact that no person has ever seen a species produced by a gradual process. Then again, no person has ever seen a giant redwood tree grow from a seed. But one can find redwood trees of all sizes and observe their incremental growth within years.

Republican politicians are welcome to their views on the relationship between faith and science, but they have no excuse to be unfamiliar with the scientific evidence supporting evolutionary theory. At a time society must confront rapidly evolving infectious diseases and threats to life-sustaining ecosystems composed of evolving organisms, understanding evolution is as important as basic literacy. We cannot afford decision-makers who are ignorant of it.

About the writer:

Robert M. Pringle is an evolutionary ecologist in the Department of Biological Sciences of Stanford University. Paul R. Ehrlich, Bing Professor of Population Studies at Stanford, is author of The Process of Evolution and The Population Bomb.