Developmental psychology was purely focused on children for a very long time. In 1920s: studies on aging started still not considered developmental psychology & In 1940s: gerontology established as research eld. Erikson (1959) proposed lifespan theory of personality development. The biopsychosocial perspective a view of development as a complex interaction of biological, psychological, and social processes. The interaction of these domains forms an overall view of the self . These four principles are foundational to the biopsychosocial approach. Principle changes are continuous over the life span only the survivors grow old individuality matters. Meaning individuals remain the same" even though they change aging individuals are increasingly self-selected people vary within and between age groups. When others look at you they don"t necessarily share this perspective you were younger unless they"re close relatives or friends other data to draw from how they were in the past.