Instincts are species-specific and individual stereotypes of behavior that are organizing on the basis of complex reflexes according to a genetic program. The most complex reflexions are formed by a sequence of complex reflexes, the completion of each of which is the beginning of the next. P.V. Simonov singled out three different classes of the most complicated unconditioned reflexes: 1) vital unconditional, 2) role (zoosocial), 3) unconditional reflexes of self-development. The second class of the most complicated unconditioned reflexes can be realized only by interacting with other individuals of the same species. These reflexes underlie sexual, parental, territorial behavior, the formation of a group hierarchy.
Instinct is an evolutionarily worked out innate adaptive form of behavior inherent in this species of animal, representing a combination of complex reactions that occur in response to irritation. Konrad Lorenz believes that instincts should be understood as specific, strictly fixed actions (movements), the same in the same situations in all the presented species. Lorenz called instincts as "a complex of fixed actions" or stereotypical behavior. According to his ideas, under the action of a number of external and internal factors (hormones, temperature, light, etc.) in the corresponding nerve centers, an accumulation of “energy of action” occur specific to a certain drive (hunger, thirst, sexual need, etc.). The growth in this activity above a certain level leads to the appearance of the search phase of a behavioral act, which is characterized by a wide variation in performance, both in a given individual and in different representatives of the same species. It consists in the active search for irritants, under the action of which it is possible to satisfy the impulse that has arisen in an animal. When stimuli are found, the final act is carried out - a fixed complex of species-specific stereotyped movements, as in one individual in each case, and in all individuals of a given species. This complex of movements is characterized by a high degree of genotypic conditioning.
Either way, instinctive reactions are innate. In the implementation of such complexes of instinctive fixed actions, the starting function is performed by external stimuli, which in their entirety create a starting situation. Each key-stimulus launches a corresponding set of programmed actions. Key-stimuli are environmental signs to which animals can react, regardless of their individual experience, with an innate behavioral act.

The study was conducted with the financial support of the Russian Foundation for Basic Research (Project 17-04-01321a).