 Notice that al-Fārābī is following Aristotle according to whom the heart is the center of the biological and even perceptive capacities of animals and human beings. The heart is relevant because it is the source of innate heat or the vital innate spirit, which spreads through the blood vessels sustaining and preserving all the parts of the body. The second major organ, the brain, regulates the heat disseminated by the heart (al-Fārābī VC: 176–177). This innate heat is the principle of life. This biological account helps explain the origin and nature of the soul. In the previous section I explained al-Fārābī’s understanding of the origin and composition of matter and its relation to the form. When referring specifically to the conformity of the human body and the origin of the rational soul, al-Fārābī holds that the conformity of this kind of body with its corresponding set of faculties is only possible when the heat of the heart reaches a certain temperature.