Aging is both a biological process and a sociological phenomenon. As a biological process, it can be seen as beginning at birth or conception and unfolding throughout the life span. In this way, biological changes affect the individual organism, leading to a variety of changes throughout life, from growth and maturation through the child-rearing years and into the period known as old-age or senescence.
Understanding these changes over time, and ameliorating those that are undesirable, is an important part of understanding aging research. Equally important is the need to understand the impact of the aging process on the individual within the context of society. What values and roles are assigned to the individual based upon chronological age? What expectations does society have for people? And are there resources available to help people meet these expectations?
As overall population aging takes place, such questions become more pressing. In the first decades of the 21st century, these are pressing questions indeed. Throughout the world—in the industrialized world and, increasingly, in poorer countries—we are seeing perhaps the greatest demographic shift ever. Life expectancies have exploded, both at birth and at older ages. People over the age of 100, once seen only rarely, have become much more common. Large percentages of the population are entering the period traditionally known as “aged,” making the traditional age pyramid much more rectangular and changing the ratios among various population segments. The traditional three-generation family is becoming stretched into four and sometimes five generations. Although often presented as a “crisis,” this demographic revolution is also one of the great successes of our time.
One of the challenges for society is deciding what this demographic change means and how we want to think about it. A quarter