During the 20th century, three polls questioned outstanding scientists about their attitudes toward science and religion. James H. Leuba, a sociologist at Bryn Mawr College, conducted the first in 1914. He polled 400 scientists starred as "greater" in the 1910 American Men of Science on the existence of a "personal God" and immortality, or life after death. Leuba defined a personal God as a "God to whom one may pray in the expectation of receiving an answer." He found that 32 percent of these scientists believed in a personal God, and 37 percent believed in immortality. Leuba repeated basically the same questionnaire in 1933. Belief in a personal God among greater scientists had dropped to 13 percent and belief in immortality to 15 percent. In both polls, beliefs in God and immortality were less common among biologists than among physical scientists. Belief in immortality had dropped to 2 percent among greater psychologists in the 1933 poll. Leuba predicted in 1916 that belief in a personal God and in immortality would continue to drop in greater scientists, a forecast clearly borne out by his second poll in 1933, and he further predicted that the figures would fall even more in the future.

click for full image and caption

Edward J. Larson, professor of law and the history of science at the University of Georgia, and science journalist Larry Witham, both theists, polled National Academy of Sciences members in 1998 and provided further confirmation of Leuba's conjecture. Using Leuba's definitions of God and immortality for direct comparison, they found lower percentages of believers. Only 10 percent of NAS scientists believed in God or immortality, with those figures dropping to 5 percent among biologists.