In modern psychologyStudies and research

Physiologists divide organic functions into three categories: nutritional functions, sensory and movement functions, and then reproductive functions. The first includes the processes of digestion, blood circulation, breathing, and excretion of waste. Together, these processes lead to tissue growth and the generation of energy and heat that the animal consumes during movement.
As for the functions of sense and movement, they are what establish the animal's connection with its external environment, and this connection is limited in its simplest manifestations to bringing what is beneficial and avoiding harm. Through the cooperation of the functions of nutrition, sensation, and movement, the survival of the individual is achieved. The duration of survival varies depending on the animal species after the individual passes through the stages of embryogenesis, childhood, youth, adulthood, and then old age. But there is another function whose signs appear after the end of childhood - that is, in adolescence - which is the function of reproduction, and its purpose is to multiply the species and prevent it from extinction and death. This distribution of functions implies great wisdom, which is that the existence of the species is the goal towards which nature aims.