Descartes and the pineal gland in animals: a frequent misinterpretation

René Descartes presented a number of reasons for his choice of the pineal gland as a logical place for the soul to interact with the physical machinery of the body. It is often stated that one of his reasons was that he believed animals do not have pineal glands, whereas humans alone possess a soul and this small structure. This is a misinterpretation of Descartes. The philosopher knew that barnyard and other animals possess pineal glands, having seen this with his own eyes. His point was that the pineal is unique in humans only because of a special function - acting as the seat for the rational soul.