For a university professor, Francisco J. Ayala spends a lot of time on the road.

An evolutionary biologist and geneticist at the University of California, Irvine, he speaks often at universities, in churches, for social groups and elsewhere, usually in defense of the theory of evolution and against the arguments of creationism and its ideological cousin, intelligent design.

Usually he preaches to the converted. But not always.

As challenges to the teaching of evolution continue to emerge, legislators debate measures equating the teaching of creationism with academic freedom and a new movie links Darwin to evils ranging from the suppression of free speech to the Holocaust, “I get a lot of people who don’t know what to think,” Dr. Ayala said. “Or they believe in intelligent design but they want to hear.”

Dr. Ayala, a former Dominican priest, said he told his audiences not just that evolution is a well-corroborated scientific theory, but also that belief in evolution does not rule out belief in God. In fact, he said, evolution “is more consistent with belief in a personal god than intelligent design. If God has designed organisms, he has a lot to account for.”

Consider, he said, that at least 20 percent of pregnancies are known to end in spontaneous abortion. If that results from divinely inspired anatomy, Dr. Ayala said, “God is the greatest abortionist of them all.”