A pipe-smoking, tweed-jacketed Oxford don saw it all coming more than 50 years ago: Scientists and politicians debating human cloning, gene manipulation, controlling our progeny—all in the name of humanity, of course.

"If any one age really attains, by eugenics and scientific education, the power to make its descendants what it pleases," C.S. Lewis prophetically warned, "all men who live after are the patients of that power." They will be slaves to the "dead hand of the great planners and conditioners."

This is ultimately the issue facing us in today's intense debates over embryonic stem-cell research, so-called therapeutic cloning, and the like. Beyond the questions argued in Congress as I write—whether embryos are humans or merely, as The New York Times puts it, "a ball of cells"—lurks the largely ignored question Lewis posed: What becomes of humanity if we become the controllers?

The biotech revolution has surged forward as the defining issue of this new century. On the one hand, it holds out great promise for medical advances enhancing life and health for all humankind. On the other, it raises unprecedented ethical issues.

Christians are not Luddites; we simply insist that science remain tethered to moral truth. But the biotech revolution is moving like a steamroller, fueled by huge potential profits, crushing everything—including moral restraint—in its path. Secular ethics, in this relativistic age, have been drained of moral content; they can be based only on utilitarianism (doing the greatest good for the greatest number) or pragmatism (doing whatever works). Thus Princeton bioethicist Peter Singer advocates infanticide for defective ...