Is it your genes or experiences that determine how intelligent you are? If a young adult woman is outgoing, does this mean she will be outgoing in late life? If people change, is it more gradual or sporadic? Is aging the same around the world? These and similar questions have occupied some of the greatest Western philosophers in history: Plato, Aristotle, Rene Descartes, John Locke, and Ludwig Wittgenstein, among many others. Four main issues occupy most of the discussion: nature versus nurture, stability versus change, conti­nuity versus discontinuity, and universal versus context-specific development. Because each of these issues cuts across the topics we discuss in this book, let’s consider each briefly.

The Nature-Nurture Issue. Think for a minute about a particular characteristic that you and several people in your family have, such as intelligence, good looks, or a friendly, outgoing personality.

Why is this trait so prevalent? Is it because you inherited the trait from your parents? Or is it because of where and how you and your parents were brought up? Answers to these questions illus­trate different positions on the nature-nurture issue, which involves the degree to which genetic or heredi­tary influences (nature) and experiential or envi­ronmental influences (nurture) determine the kind of person you are. Scientists once hoped to answer these questions by identifying either heredity or environment as the cause of a particular aspect of development. The goal was to be able to say, for example, that intelligence was due to heredity or that personality was due to experience. Today, how­ever, we know that virtually no features of life-span development are due exclusively to either heredity or environment. Instead, development is always shaped by both: Nature and nurture are mutually interactive influences.

Studying Adult Development and Aging 17