An important aspect of the nineteenth century debate on the relationship between science and religion concerned the popularity of deterministic views among scientists. An integral part of Comte's positivism, the idea of immutable laws that determined natural and social phenomena became an increasingly prevalent component of scientific perspectives in the Darwinian era. Referring to this tendency as 'scientific fatalism,' critics likened it to Calvinist predestination, which transformed the debate into one involving polemics about different branches of Christianity as well. This paper focuses on a neglected aspect of this debate, namely, the role that references to Islam and Turks played in it. 'Mohammedan fatalism,' already a common theme in justifications of colonialism, promptly became a tool with which to condemn new scientific views. Comparing French, British, and American writings on the topic, the paper illustrates that while there emerged approaches that praised the fatalism of Muslims while making a case for scientific determinism, most scientists and thinkers resorted to condemning the fatalism of Muslims in order to distinguish their views from it. In this respect, the paper demonstrates how political and religious discourses played a significant part in the shaping of scientific discourse in the Victorian era.