ABSTRACT
Every science which is more than a simple agglomeration of assumed facts, but which tries to build up a logical construction of theories and hypotheses that bind such facts together, has generally one or more central problems to which all these theories and hypotheses are related. For animal psychology this central problem is that of animal instinct. In the philosophy of the man in the street the view may often be heard that the animal is impelled to its acts by "instinct," man on the contrary by "intelligence." According to this way of thinking, instinct comprises all the psychical faculties of the animal; it is, perhaps, even the only psychical quality with which the animal is credited. Instincts and instinctive actions are characteristic of the species to which the animal belongs. All members of a species, or of a wider systematic group of animals, in similar circumstances behave in a similar instinctive way.
