Human development is a lifelong process beginning before birth and extending to death. At each moment in life, every human being is in a state of personal evolution. Physical changes largely drive the process, as our cognitive abilities advance and decline in response to the brain's growth in childhood and reduced function in old age. Psychosocial development is also significantly influenced by physical growth, as our changing body and brain, together with our environment, shape our identity and our relationships with other people.
Although various scholars define physical development in slightly different ways, most generally break the process down into eight stages that include infancy; early, mid and late childhood; adolescence; early adulthood; middle age and old age. In recent years, as people have lived longer, some have added "very old age" to this list. At each stage, specific physical changes occur that affect the individual's cognitive and psychosocial development.
Cognitive development refers to the acquisition of the ability to reason and solve problems. The main theory of cognitive development was developed by Jean Piaget, a Swiss developmental psychologist. Piaget broke childhood cognitive development into four stages spanning from birth through adolescence. A child who successfully passes through the stages progresses from simple sensorimotor responses to the ability to classify and create series of objects and eventually to engage in hypothetical and deductive reasoning, according to "The New Dictionary of Scientific Biography."
The primary theory of psychosocial development was created by Erik Erikson, a German developmental psychologist. Erikson divided the process of psychological and social development into eight stages that correspond to the stages of physical development. At each stage, according to Erikson, the individual faces a psychological conflict that must be resolved in order to progress developmentally. Moving from infancy to old age, these conflicts are trust versus mistrust, autonomy versus shame and doubt, initiative versus guilt, industry versus inferiority, identity versus role diffusion, intimacy versus isolation, generativity—that is, creativity and productivity—versus stagnation, and ego integrity versus despair.
According to the U.S. Department of Health and Human Services, or HHS, "Development is the product of the elaborate interplay of biological, psychological, and social influences." As children develop physically, gaining greater psychomotor control and increased brain function, they become more sophisticated cognitively—that is, more adept at thinking about and acting upon their environment. These physical and cognitive changes, in turn, allow them to develop psychosocially, forming individual identities and relating effectively and appropriately with other people. Thus, as described by the HHS, human development is "a lifelong process of growth, maturation, and change."
The importance of physical, cognitive and psychosocial development becomes apparent when a person does not successfully master one or more of the developmental stages. For example, a child who fails to achieve basic milestones of physical development may be diagnosed with a developmental delay. Similarly, a child with a learning disability may fail to master the complex cognitive processes of a typical adolescent. A middle-aged adult who does not successfully resolve Erikson's stage of generativity versus stagnation may experience "profound personal stagnation, masked by a variety of escapisms, such as alcohol and drug abuse, and sexual and other infidelities," as stated by Nursing Theories. Thus, the stakes are high for all humans as they tackle the developmental tasks they confront at every age.