An interview with Francisco J. Ayala
Francisco J. Ayala, a professor of evolutionary biology and philosophy at the University of California-Irvine, is both an expert in the field of evolution and its ardent defender. From serving as an expert witness in court battles over the teaching of evolution in public schools to writing a letter defending evolution to Pope Benedict XVI just last year, Ayala has been a tireless advocate of what he calls the "fact" of evolution, arguing strongly against the theory of intelligent design, whose advocates claim that evolution leaves no room for God.
But evolution and religion need not be adversaries, says Ayala. "Science can neither endorse nor reject religious beliefs," he writes in his book Darwin and Intelligent Design (Fortress), arguing that "we may accept [evolution] without denying the existence of God or God's presence in the universe."
Ayala, winner of a 2001 National Medal of Science, has his work cut out for him: A June USA Today/Gallup survey of 1,003 adults found that two thirds of those polled believe that humans were created by God about 10,000 years ago, while only 52 percent say that humans evolved over millions of years.
When scientists talk about the theory of evolution, what do they mean?
Evolution is the history of living things, the origin and development of life. We used to study it by means of morphology, paleontology, and fossils, but now we also use DNA because it has much more information. With DNA we can now ascertain the evolutionary history of an organism. We can now trace the history of living organisms all the way back to a single universal common ancestor.
Evolutionary theory also includes the mechanisms by which evolution operates. The key process is natural selection, which accounts for adaptation. Natural selection is one of the greatest discoveries in the history of science. It is the process that explains why we have eyes for seeing, hands for grasping, legs for walking.
The evidence for evolution is so strong that we often speak of it as the "fact" of evolution. It is no longer an issue that occupies scientists nowadays, because the fact that evolution has occurred and accounts for the history of organisms is certain, just as science is certain that the Earth revolves around the sun.
When scientists refer to evolution as a theory, does that mean it might not be true?
Theory in science does not mean unsupported opinion but rather a well-established body of knowledge, which includes concepts and explanations that have been tested by scientific method. When scientists refer to what is called a theory in common language, they call it a hypothesis, an assumption or guess that has yet to be fully tested. But the word theory is never used in science to suggest something like a hunch.
How can scientists be so certain about the "fact" of evolution?
As you may have read in the papers or seen on television, we can use DNA to find out the identity of the father of Anna Nicole Smith's daughter. Most people know about convicted prisoners whom DNA has proved innocent.
By looking at DNA we can also reconstruct the history of evolution because DNA carries all the genetic information of living organisms. DNA changes gradually over time through mutations, which are fairly rare. Natural selection determines which of those mutations are beneficial and become established, and which ones are eliminated.
DNA has an enormous amount of information. We inherit 3 billion nucleotides (bits of DNA each signified by one letter) from each one of our parents, what we call one genome. The letters that make up one human genome alone would fill about a thousand volumes the size of a Bible. So there's a lot of information to compare organisms with each other, which allows us to reconstruct their evolutionary history. We can keep studying more DNA until we get greater and greater precision. …