As was in evidence from a recent Valley Voices commentary in this newspaper, there unfortunately remain widespread misconceptions regarding not only whether evolution occurs, but about the meaning of the word theory.

We and our colleagues at Fresno State are profoundly concerned that the public continue to be subjected to misinformation and poorly educated bias. Our mission is to educate in the sciences and mathematics, and we have a responsibility to provide outreach to the local community in pursuit of that mission. A scientifically illiterate populace will result in the United States being rapidly outpaced by the rest of the world.

Evolution is the change of organisms over time, observed most fundamentally in alterations of genes. This is a fact, directly observed in any organism that is investigated, and supported by thousands of research studies.

The best known mechanism for how those differences result in gradual change of populations and ultimately lead to the diversification of life is natural selection.

Natural selection was, of course, originated and articulated by Charles Darwin more than 150 years ago, and it is this mechanism that is theoretical, not the occurrence of change.

However, a theory in science is an extraordinarily powerful statement, supported by massive amounts of evidence -- the only scientific construct more fundamental than a theory is a law.

Natural selection remains the mechanism that best explains the data we gather, and it is worth considering its formulation and impacts. So, what did Darwin contribute to biology and society?

First, the publication of "On the Origin of Species ..." quickly convinced biologists and many others that living things change over time, and are connected by the branches of a tree-like lineage. In other words, they evolved from common ancestors.

This simple concept has had a profound influence on how we view the world and ourselves in it. We are simply one of a great many twigs on the tree of life. Darwin's great champion, Thomas Henry Huxley, said simply, "How stupid of me not to have thought of that."

Most recently, molecular biologists have found that DNA contains a record of the changes in organisms as they evolved. For example, closely related species such as humans, dogs and other mammals share about 90% of the same genes, whereas more distantly related organisms, such as the yeast cell, share about 50% of their genes with humans.

Second, Darwin proposed a mechanism for this change over time. This idea had a rougher road to acceptance, and only after the development of population genetics were most biologists convinced that Darwin was correct. Biologists, like all scientists, are highly skeptical until they see adequate supporting data.

But why do we consider evolution the central tenet of biology?

Because it integrates the science. Evolution is to biology as the periodic table is to chemistry, plate tectonics is to geology and quantum mechanics is to physics. None of these disciplines make any sense without these core ideas.

Natural selection makes sense of much of modern medicine. Just as we explain the origin of antibiotic resistance in bacteria, we can explain why antiviral drugs work over the short term but become ineffective over the long term. Our knowledge of how viruses evolve is the basis for great concern about the H5N1 strain of the influenza virus that shifts from pigs to birds to humans.

Alternative ideas have been tested over the past two centuries, including special creation and versions of "intelligent design."

Biologists rejected these alternatives decades ago. They have no explanatory power, no credible evidence, and have long been regarded as non-science, as they invoke supernatural causation, which is not considered by scientists.

The Biology Department at Fresno State could no more teach biology without evolution than we could without physiology, ecology or genetics.

As the great 20th Century geneticist Theodosius Dobzhansky stated in his 1973 essay of the same title: "Nothing in Biology Makes Sense Except in the Light of Evolution."