ABSTRACT
Reactions are the fundamental elements out of which all human and animal behavior is composed, both in the simplest and in its most complex forms. In animals that possess a nervous system, reactions tend to assume the form of what is known as a reflex. For the simplest observation of human or animal behavior, it suffices to note that behavior itself consists in reactions that originate in different ways. Some reactions are inherited or innate, and seem to be conferred on the child at the very moment of birth, or arise as the child grows up without any training or outside action. The general principle underlying the origin of the instincts was established and elucidated by Charles Darwin in his study of natural selection. In this sense, there is no essential difference between the origin of the useful inherited forms of animal organization and the behavior of animals. As studies have shown, highly complex forms of conditional reflexes are possible.
