On the incomplete architecture of human development: The fourth age

Drawing on both evolutionary and ontogenetic perspectives, the basic biological-genetic and social-cultural architecture of human development across the life span is outlined. Three governing principles are involved. First, evolutionary selection evinces a negative age correlation and, therefore, genome-based plasticity and biological potential decrease with age. Second, for growth-aspects of human development to extend further into the life span, culturebased resources are required at ever increasing levels. Third, because of age-related losses in biological plasticity, the efficiency of culture is reduced as life-span development unfolds. Joint application of these principles suggests that the life-span architecture becomes more and more incomplete with age. With regard to life-span outcomes, degree of completeness can be defined as the ratio between ga;ns and losses in functioning. Two examples are given to illustrate the implications of the lifespan architecture proposed. The first is a general theory of development involving the orchestration of three component processes: selection, optimization, and compensation. The second example considers the task of completing the life course in the sense of achieving a positive balance between gains and losses for all age levels. This goal is more and more difficult to attain as human development is extended into old age.