Probabilistic Darwinism: Louis Agassiz vs. Asa Gray on Science, Religion, and Certainty

Despite the professed harmony of science and religion in early to middle nineteenth‐century culture, scientific practice gradually veered away from confirmation of religious assumptions. This trend culminated in the shock of Charles Darwin's theory of species development, which troubled many scientists and religious believers both for its explicit naturalism and for the unprovable probabilism at the heart of its method. Two key players — and antagonists — in the reception of Darwinism in America, Louis Agassiz and Asa Gray, actually agreed in their assessment of the probabilistic quality of Darwinism, but they split over how much uncertainty to wel‐come into their science and their religion. Agassiz became intellectually marginalized because he continued to demand certainty, while Gray’s acceptance of uncertainty represented a growing trend among intellectuals of science and religion.