The vitalistic doctrine of Aristotle and Galen, in which the soul is an indissoluble part of the body, was undisputed throughout most of the Middle Ages. The first radical change came with Telesio, who developed philosophic naturalism in which the soul has a reality of its own, though it is connected to the body. The definitive change came with Descartes, who believed that all biologic phenomena can be explained by the laws of mechanics, and only man is distinguished by the possession of a soul. For the next 300 years, this mechanistic view would be challenged by a new vitalism, in which the ‘vital force’ has an existence in its own ri