One consequence of [Carl] Sagan’s religion of the cosmos was that he was actively committed to the cause of animal rights. And quite logically so. For if humans evolved from beasts, there can be no intrinsic difference between them. It would be just as cruel and immoral to kill a cow as to murder a person. “In my writings,” Sagan said in a Parade magazine article, “I have tried to show how closely related we are to other animals, how cruel it is to gratuitously inflict pain on them.” As a result, he was adamantly opposed to using animals for medical research. For if animals have the same value as humans, how can we justify expending their lives to save humans.
But on this issue, Sagan bumped up against reality in a very painful way. In 1994, he discovered that he had myelodysplasia, a rare blood disease. With possibly just months to live, he was told that his only chance for survival was an experimental bone-marrow transplant. But there was one catch: The procedure that might save his life had been developed by research on animals—the kind of research Sagan passionately opposed.
Sagan faced an excruciating dilemma: Should he remain true to his naturalistic philosophy and reject the marrow graft as something acquired by immoral means? Or should he agree to undergo the medical treatment in hope of saving his life, though it meant acting in contradiction to his moral convictions.
Sagan didn’t take long to reach a decision: He underwent three bone-marrow treatments, which did extend his life for a time (though he ultimately succumbed to the disease and died in 1996). At the time Sagan wrote the Parade article, he was still, in his words, “very conflicted” over the choice he had made. He recognized clearly that his decision to accept the treatment was a practical denial of his naturalistic worldview. But when he came up against reality, he abandoned his naturalistic road map and, whether he admitted it or not, implicitly shifted to the biblical road map, which says that humans do have a value transcending that of plants and animals.
— Charles Colson and Nancy Pearcey, from How Now Shall We Live?, p. 99