From Wallace Arthur's Creatures of Accident (2006), chapter 20, “Big Questions”, pages 231, 232.

…But with regard to realms which, by definition, permit no examination and thus provide no evidence, I find nothing to guide me. I see no more reason for a rational scientist to be a committed atheist than to be a committed theist. I do, in contrast, see every reason for such a person to be a committed agnostic, if that is not a contradiction in itself.

We owe the word "agnostic" to the man who earned the nickname Darwin's bulldog for his fierce defense of evolution against diverse nineteenth-century critics – Thomas Henry Huxley. It is hard to overestimate Huxley's importance in both respects. The initial progress toward widespread acceptance of evolution by natural selection would have been slower by far without Huxley's articulate and impassioned advocacy. And what I regard as the only honest worldview would have continued to be anonymous without the name that Huxley gave it, and so to be less visible beside its faith-based counterparts of theism and atheism.

It might seem odd to categorize atheism as being faith-based. Yet the more I think about it, the less I am able to see it in any other way. No intelligent and honest person could believe, any longer, in a Creator who supposedly made the world and all its creatures some six thousand years ago, as was argued by the seventeenth-century Anglo-Irish archbishop James Ussher. In the twenty-first century, the possible Creator that we can decide to believe in or not, or to remain agnostic about, is an altogether more elusive one. The existence of a Creator inhabiting as-yet-unknown dimensions, whose only involvement with the universe was to launch it forth from nothingness (why?), who does not direct the evolutionary process that eventually started on at least one planet, and who does not reveal herself to humans (unless after death?), is impossible to decide upon with the evidence available to us. So belief in herabsence is as much an act of faith as belief in her presence. Agnosticism, on the other hand, represents a lack of belief in either direction. More broadly, it represents a philosophical stance in which we refuse to believe in something (or its lack) without adequate evidence.

This stance is one of the foundations of science. Through it we have come to understand how and when complex creatures arose, and much else besides. The reliance on evidence, and the lack of reliance on faith or authority, have been essential ingredients in the progress of human thought. No book is infallible. This applies to the holy books of all the world's religions, and to all scientific books, including, of course, this one. We owe it to ourselves to reflect upon what we read, and not to take anyone's word as unchallengeable. As Huxley said: "The ultimate court of appeal is observation and experiment, and not authority."

Not only is the progress of human knowledge important, so is the life of every individual. Intolerant faith has often resulted in the taking of lives. We have already discussed the Crusades of almost a thousand years ago and the terrorist bombings that have become an unfortunate feature of our present-day world. These takings of innocent lives were, and are, perpetrated by people who claim allegiance to one or another religious faith. But we should also remember that a mere few decades ago, millions were sent to their deaths in Stalinist Russia, many of them because their religion offended the atheist faith of the Soviet regime. To my knowledge, not a single human life has ever been taken in the name of agnosticism.