Part 3 of our text explores the development of personality over the life-span. In chapter 5, we review theoretical models of life-span development. Chapter 6 examines biological mechanisms in personality functioning; we consider both genetic influences and specific brain systems underlying individual differences. Chapter 7 explores the role of interpersonal relations in the development of personality, and Chapter 8 reviews the broader social systems within which personality develops.

This part of our text builds on our earlier discussions. We have defined personality as the complex system of psychological structures and processes through which people regulate their actions and experiences. This system conveys to the individual and to observers a sense of the person's identity, continuity, and uniqueness. Personality is constructed through interactions between the organism and the social environment. As we have emphasized, people do not passively absorb environmental influences but actively shape and interpret them. It is from this perspective that we now address the development of the individual's capacities, preferences, and tendencies.

Our coverage includes a wide-ranging and somewhat complex set of determinants of personality development. Such complexity is necessary because development is not a simple matter. It “involves multidimensional and multidirectional elements in constant states of organization and reorganization” (Hartup & van Lieshout, 1995, p. 659). Due to this complexity, development can proceed in a number of different directions from any given initial state and, conversely, different development routes can lead to similar outcomes (Baltes et al., 1998).