Life Course Perspective on Adult Development

A life course perspective on adult development is one that sees continuity between phases of adult development. In general, the relative rank order of individuals during childhood (e.g., the smartest kid in the class, the fastest runner on the track) is maintained throughout life. This generalization is modified by the area of function (e.g., intelligence, cognition, personality), the level of social class or educational attainment, and the physical health status of the individual. These three areas influence each other, making for a complex set of pathways that need to be understood.

Furthermore, there are relatively few studies that have more than 50 years of data, so that studies that started with individuals in their 20s can now speak to what happens by 70 years of age and studies that started with individuals 70 years of age can speak to what happens by 100 years of age. Studies with serial cohorts can provide some important hints about how adjacent stages of the life span are related, and studies that start during middle or later life with archival data about levels of functioning earlier in the life cycle can also add to our understanding. It is rare to have longitudinal data that follow large cohorts of persons into extreme old age when they are no longer capable of being tested in the laboratory with the same set of measures employed earlier, and those that do often employ proxy respondents. Measurement tends to shift from assessments of intellectual functioning to mental status measures and from physical performance to activities of daily living (ADLs).

First and foremost, work from longitudinal studies is preferred. Cross-sectional studies are an important first step in figuring out what is worth studying longitudinally. Indeed, when similarities in performance and behavior are seen cross-sectionally, that is the [Page 325]exception and worthy of comment and future study; however, that is rarely the case. Age is not an explanatory variable but rather a marker of the passage of time set within a particular sociohistorical context. The actual time of measurement of the status of the individual and the status of knowledge in medicine both contribute to an understanding of aging and health associations. The goal of adult developmental psychology is to replace age with a variable with more explanatory power. Relationships between aging and health (or, more accurately, aging within levels of physical health status) determine the experience of aging for most persons and their family members.

The content of this entry revolves around a set of important questions:

• 1
  Where do we see continuity, and where do we see change, in psychological development? The literature would suggest that there is significantly more continuity in personality and social functioning than in cognitive and intellectual functioning. Personality is maintained even with the onset of memory disorders such as Alzheimer's disease for functions that do not depend on memory (e.g., conscientiousness), and social functioning is maintained until the final phases of impairment. Levels of cognitive and intellectual performance decline earlier if speed is involved in the function tested, such that vocabulary and crystallized intelligence are preserved even during extreme old age. Diseases such as hypertension, heart disease, and diabetes have been implicated in changes in cognitive and neuropsychological performance, and personality constructs such as hostility and anger have been related to the earlier development of hypertension, heart disease, and diabetes.
• 2
  How predictable is the life span? Within a stage of development (young adulthood, middle age, and old age) where we have data, predictability is quite reasonable.
• 3
  How long do variables need to predict to satisfy the criteria of a life course or life span perspective? This is really a theoretical question, and new data from infancy are challenging our notions of life span on the power of variables such as birth weight to have consequences for the rest of the life span.
• 4
  How important is age as a variable? Age is the best summary variable that we have. It is important to know the actual time of measurement of the age because it means something different to be 40 years old in 1960 than it does to be 40 years old in 2000. Thus, understanding age by time of measurement is a powerful combination. The birth cohort of the individual also conveys important information. Those born between 1946 and 1964—the baby boom cohort—have experienced their aging differentially because they are such a large cohort that society has always adjusted to make room for them. The aging of this cohort will have a profound impact on society.
• 5
  Is there an age where the life span no longer makes any sense? Life span developmental psychology today has less to contribute to geriatrics than it could or should in the future. Geriatric syndromes such as frailty are not really seen earlier in the life cycle.
• 6
  What do we know about “extreme” aging and super-centenarians? Data from centenarians are being pooled on a worldwide basis. The Rule of 3 appears to apply; one third are in outstanding shape, one third are plagued by the age-related declines in sensory and motor functions assumed, and one third are moribund given the peculiar nature of our health care systems to maintain survival independent of independent functioning. Research on the genetic determinants of extreme aging with biological and psychosocial data is progressing, but no answers are yet available.
• 7
  What is normal aging? This question is probably best answered within levels of physical disease. Those with specific diseases may well have predictable life courses that are different from those of their age peers with different diseases and combinations of diseases.
• 8
  What role does the development of disease play? It plays a central role, but we do not yet have sufficient data to specify this.
• 9
  What role does the socioeconomic status (SES) gradient play in aging? The SES gradient seems to suggest that those at the lower end of the economic distribution tend to accumulate diseases earlier in [Page 326]their life span than do those at the upper end. Furthermore, treatments for disease may also be different for the SES groups. However, for those who survive into extreme old age, there may be a crossover effect.
• 10
  How much can be attributed to aging and individual process, and how much is dependent on the social milieu? This may depend on the age of the person. Later in the life cycle, the social milieu may increase in importance. Thus, studying aging in couples and families may be more important during the final quarter of the life cycle than earlier. It is also important to remember that the size of a generation may be 15 to 40 years wide. Thus, a person 40 years of age may be a grandparent while having living parents and grandparents.

In sum, the life span approach to adult development has been useful in understanding development of the individual up to the time of the oldest old (approximately 85 years of age). Current work should extend our understanding of the life span for the final 30 years up to 115 years of age.

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