Paul B. Baltes, developmental psychologist and Distinguished Professor of Psychology at the University of Virginia, established six principles of developmental lifespan psychology. When one delves into the field of human development, one must consider these principles.
Human development is a lifelong process. Individuals have the potential for development throughout their lifespans. There is no logical reason for an individual to reach a plateau or to decline as he ages. Development is not set at birth but is related to experiences throughout the lifespan. Aging, according to Baltes, begins with the beginning of life and so need not be the cause of decline.
Development in human beings crosses multiple dimensions. Social, emotional, cognitive, and biological factors are all involved in the development of individuals. An individual's condition can be caused by multiple factors. For example, diabetes may be caused by heredity, diet, environmental factors, injury, or other factors.
The progression of development is not always forward. The individual will experience gains and losses at all ages. However, there are more developmental gains in the earliest years of life than in the latest years.
Research into human development must involve a multidisciplinary approach. Medical, psychological, and behavioral research must intertwine in order to form the clearest picture of human development. This research must include studying humans of all developmental levels.
The study of human development must allow for the plasticity or variability of behavior and development in an individual. Plasticity refers to an individual's ability to change or adapt. For example, a child who loses both his arms may learn to perform multiple functions with his feet. This adaptation will lead to changes in the development of muscles and other body systems. Physical, environmental, and psychological challenges may lead to individual variance in development. There is typically a loss of plasticity as one ages, however.
Development does not happen in a bubble. Humans do not live in isolation. An individual's development is influenced by the context of his environment. This context includes his family, physical environment, educational influences, societal norms, and cultural context. Development is also tied to historical time and place. For example, a twelve-year-old female living in Colonial America would develop significantly differently than the same girl in Modern America. Nutrition, gender norms, educational differences, and other factors would influence each child's development in drastically different ways.