Since I was a child, I have always been fascinated by living things, but I believe all human beings are. I truly liked cats, and I asked myself many questions about their behavior, how they are made, and the difference between a cat and an inanimate object. The answer then seemed banal: the cat responded when I caressed it; it responded to external stimuli, whereas an inanimate object did not do all this. This question of mine about what life is and which for me had a banal solution is a question that men have been asking themselves for thousands of years, and even today, we do not have a precise definition. For example, for Aristotle, living beings, unlike inanimate beings, had three types of soul: vegetative, animal, and rational (in the case of human beings). George Erns Stahl and others defined the doctrine of vitalism in the seventeenth century. According to vitalists, living organisms differ from nonliving organisms because they are equipped with nonphysical elements, and they also believe that the organic matter, of which we are made, cannot be derived from the inorganic matter, of which nonliving beings are made.