Developmental psychology

Developmental psychology is the branch of psychology that studies how and why the human mind grows, changes, and adapts over the course of a lifetime. Its subject is the systematic psychological change that people undergo as time passes, understood as a continuous, global and flexible process in which the individual reaches states that are more complex than those before.

The field was at first concerned mainly with infants and children, but it has since expanded to adolescence, adulthood and old age. Its roots lie in the eighteenth and nineteenth centuries: Jean-Jacques Rousseau described stages of growth in Emile, John Locke held that all behaviour is acquired, and Charles Darwin's work changed the way human development was understood. Towards the end of the nineteenth century, psychologists such as G. Stanley Hall looked for parallels between individual development and the evolution of the species. The discipline took independent shape in the twentieth century, taking firmest root in the United States.

Researchers distinguish three major dimensions: physical, cognitive and socio-emotional development. Within them the field studies topics such as motor skills, language, moral reasoning, personality, identity and self-concept, among others. To explain these changes, the discipline sets pairs of factors against each other: continuity versus discontinuity, heredity versus environment, and the normative versus the idiographic, that is, what is common to all people versus what is unique to each one.

The explanations offered have been varied. Sigmund Freud proposed psychosexual stages; Jean Piaget described qualitatively distinct phases of children's thinking; Erik Erikson outlined eight stages of psychosocial development, each with its own crisis; Lev Vygotsky emphasised the role of culture and social interaction; and Urie Bronfenbrenner proposed an ecological model that places the individual within nested, interrelated layers of environment. Some of these models are incompatible with one another, and this plurality is now seen as a source of richness rather than confusion.

A current debate pits biological essentialism against neuroplasticity, and stage theories against dynamic systems approaches, which see development as a process without fixed phases. Present-day studies seek to understand how life transitions and biological factors shape behaviour, paying attention as well to the historical, socioeconomic and cultural context in which each person grows.