Introduction

Aging begins the moment a person is born. A baby develops and matures into an adult. Then, at some point, the aging process changes. The person begins a decline in function that ultimately leads to death—what people usually think of as aging or growing old. The technical term for this decline in function that ends in death is senescence.

Science can provide information about changes in the body that lead to aging and death. Science can determine how some of the changes occur. But two basic mysteries remain: whether aging and dying have a purpose and, if so, what that purpose is. Throughout history, people have responded to these mysteries by searching for a "fountain of youth" that will prolong the time spent as vigorous, healthy young adults. And the search continues as researchers look for ways to slow or reverse the aging process.

Some progress has been made in the search. During the last century, life expectancy for people in the United States has greatly increased. As a result, what people consider to be old age has changed dramatically. Improvements in life expectancy occurred in two stages. First, death during childhood has become less likely, largely because sanitation has improved and because vaccines and treatments for childhood diseases, such as antibiotics, were developed. Second, disease and disability have become less likely to develop or have been postponed in older people because health care and approaches to prevention have improved. In spite of these improvements, even the healthiest and luckiest people do not live beyond about age 130.

See the sidebar Looking for the Fountain of Youth.