Development

The (human) life cycle and several aspects of development, such as the fertilization of plants, the grafting of fruit trees, and the principle of generation, were already known in antiquity. As with so many other areas of knowledge, it was Aristotle who summarized existing knowledge and by adding his own observations created the first inclusive theory of development. Aristotle expressed his conception of development in De generatione animalium (The generation of animals) and in his whole corpus of zoological writings, and development played an integral part in his overall science and philosophy. Aristotle's view of the world was intrinsically dynamic, based on matter and change. Matter is always structured. Form is the realized potential of matter, its entelechy, which is already present within it. In organisms, according to Aristotle, the potential form (entelechy) is gradually realized in the course of development. This dynamic process of development, as well as the resulting organism, requires all four causes of the Aristotelian physics: the material, formal, efficient, and final causes. In embryological development, the female fluid, the menstrual blood, contributes the material cause on which the semen acts, providing the initial stimulus for the dynamic sequence of development. In the course of development the combination of male and female fluids allows the formal and efficient causes to shape the emerging potential of the organism, its telos. This entelechy of the organism, however, has been present from the very beginning as the potential of this particular form of matter (the combination of male and female fluids). In later periods the Aristotelian entelechy has often been identified with the notion of a "soul," but for Aristotle entelechy is not something separate that directs development from the outside, but rather is always already present within the emerging organism as its potential to be realized gradually.