Development is systematic change over time. In humans, development is the sequence of physical and psychological changes that occurs as people age. Scholars have studied human development with regard to physical growth and maturation, motor functioning, perceptual capacities, cognitive capacities and skills, emotional repertoire and functioning, social relationships, moral capacities and tendencies, and psychopathology, among other attributes. Specific examples of development include the development of the brain in both structure and function, improvements in vision in the first months of life, infants’ advancement from crawling to walking, children’s acquisition of memory strategies, toddlers’ acquisition of social emotions such as guilt, young children’s progression from parallel play to social play, and changes in moral reasoning in adolescence and adulthood.

Changes considered to be developmental are typically progressions that result in enhanced, more complex, and more organized structures and functioning. Human prenatal development, from zygote to embryo to fetus, exemplifies such a progression. Toddlers’ developing language abilities are similarly progressive, enabling children to better interact with their caretakers and more clearly express their needs. Adolescents’ improved  logical  reasoning  permits  a more comprehensive and systematic consideration of hypothetical situations. However, regressive changes may also be considered developmental, such as the lessening of visual acuity in older individuals that results from aging eye structures. This example further illustrates that development can be viewed as lifelong. Although physical and psychological development is most obvious in infancy and childhood, changes occurring later in the life span have been characterized as development. Changes occurring in early, middle, and late adulthood in relationships, intimacy, memory, and perception, among other topics, have been the focus of developmental research. Developments in adulthood include both losses, such as those with regard to perception, and gains, such as the acquisition of wisdom.

Scientific efforts to understand physical and psychological  development  are  directed  at  description and explanation. Characterizations of development vary with regard to whether development is viewed as continuous or discontinuous, that is, whether changes are gradual, quantitative, and incremental, or whether they are qualitative and stage-like. A child who becomes a baseball player might be described as gradually learning the required skills through practice. A child who, in time, judges that a ball of clay rolled into a snakelike form has not changed in amount might be described as having advanced to a qualitatively different stage of reasoning. Besides differing on the issue of continuity, developmental accounts differ as to whether development occurs in universal sequences or whether there are multiple courses of development, such as seems to be the case when children develop varying views of the relationship between individuals and society depending on the cultural context in which they are raised.

A third aspect of development that interests scholars is its determinants. Historically, theorists have disputed  whether nature or nurture is most responsible for developmental outcomes, but contemporary accounts concur that development results from interplay between endogenous forces, such as genetic constitution, and exogenous forces, such as environmental context. However, accounts continue to vary in their emphases on these influences and in their assumptions about how the factors interact, inspired in part by historical ideas from embryology and evolutionary theory as well as from early psychology. Jean Piaget’s theory of cognitive development, for example, explains the increasing complexity and integrated organization of children’s thinking in terms that are reminiscent of biological explanations.

Because change is the essence of development, developmental scholars often employ research methods that compare individuals of different ages (cross-sectional designs) or that permit repeated observations over time (longitudinal designs). Sometimes these research designs are combined to afford a comprehensive examination of development.


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