Louis Menand's book "The Metaphysical Club," published earlier this year, charts the lives, thought and legacy of four extraordinary American thinkers, Oliver Wendell Holmes, William James, Charles Sanders Peirce, and John Dewey. For these men, and for their generation, all moral assumptions were turned upside down by Civil War, while their view of the universe was reconstructed by the publication of "The Origin of Species," in which Charles Darwin laid out his theory of evolution.

Menand's book tells the story of how these men led a revolution of ideas, finding their way out of the intellectual confusion left by the war. The result was a philosophy they called Pragmatism, which deeply influenced the 20th century's approach to law, education, politics and faith. Menand talked to Beliefnet recently about evolution, religion and science in this critical, but often overlooked, period in American history.

The period you write about-from the Civil War to the early 1900s--was really when science and theology part company.

I think they split right after the Civil War. You can see it in the history of higher education. Before the war, a university's religious position defined its curriculum, who the faculty were and what they did. After the war, the emphasis is on scientific research. Universities were happy, after the war, to sponsor research that wasn't expressly religious--though they didn't want it to be irreligious--and to separate those activities they associated with religion. So there is this kind of decorum that says science is about things that we measure and add up, and religion by definition is metaphysical and we can't talk about it in a scientific way.

That's been the case ever since. Science and religion just don't hook up. Recently there's a lot of interest in getting those two fields hooked up again, but for a long time they haven't been.

There's a stunning moment in "The Metaphysical Club" when the great 19th century naturalist Louis Agassiz gets his comeuppance in a debate at Harvard. Agassiz, who had his doubts about evolution, insisted God had created the world pretty much as we found it. In a debate at Harvard, Agassiz is told, "You're scientific position can't be argued. It's a matter of faith." It feels like a knockout punch, for Agassiz, but also for faith-based science.

But it's interesting to note that Agassiz wasn't particularly religious, but he believed in the Creator, and he used that belief to explain the natural world. It was an argument that worked for him by the canons of an earlier era, in which theology and science were not thought of as discreet pursuits. It was natural that to him that his religious instincts would be confirmed by the way the world was organized. His opponent in that debate, Asa Gray, was actually quite religious. But Gray belonged to a different scientific world, in which you accumulated data and subject it to statistical analysis. He thought that Agassiz didn't know how to do that, so he wasn't practicing science anymore.

Agassiz couldn't see the other way of doing things. It just didn't make sense to him. And suddenly one of the leading naturalists in the world wasn't on the map after 1860. It's an interesting moment. And reading Agassiz today, you do feel that he falls back on his faith, and it is a trump card that you start losing respect for after a while.

The battle over evolution is captured for us today in the so-called Monkey Trial. It's the Bible versus biology. But the first generation to read Darwin didn't worry so much about the literal truth of the Bible as the idea of a divine order. Darwin blew their mind because he was saying the universe wasn't orderly, it was incidental.

Suddenly the universe is not headed in any particular direction. Changes in the environment and in the gene pool create changes in the organism, and it can swing one way of the other indefinitely.

A lot of scientists and philosophers tried to find some consolation in evolution theory by saying that this is just the process by which God has provided to make progress toward some goal.The philosopher Charles Sanders Peirce's whole mission after reading Darwin was to wed an orderly, static idea of the universe with the insights of Darwin into the role chance. He said general laws of the universe are subject to chance variation. They evolve over time and are not permanent. They change as the universe changes. At the same time, he felt that ultimately chance would be eliminated and the universe would be subject to perfect laws. In the long run, everything would conduce to an orderly system.

Now William James and John Dewey didn't think that, and that's what makes them Pragmatists. What they learned from Darwin was that the universe is unfinished. The way we live now is the way we'll always live, without knowing what's going to happen tomorrow, or whether our hypotheses are true.

Chance, they said, is an element of existence and it won't go away.