Asa Gray (1810-1888), a Harvard botanist, was America's foremost interpreter and defender of the ideas of Charles Darwin and, like Darwin, a proponent of theistic evolution. His colleague on the Harvard faculty, Swiss-born paleontologist, Louis Agassiz (1807-1873), became America's major opponent of the ideas of Charles Darwin. On the basis of his studies in Europe and North America, Agassiz believed in the 'doctrine of sudden and catastrophic change,' rather than that of evolutionary progress. This study compares the lives and philosophies of these two American Congregationalists who were teaching scientists at the same time on the Harvard faculty and asks how they could co-exist as members of the same mainline American denomination. The paper indicates how theistic evolutionists and creationists can learn how to live together both on campus and in the church.