Is there a limit to the number of years that a person can expect to live? Can changes in life-style add years to one's life? Throughout history people have sought answers to these questions and others. Various myths offer the hope of great longevity. In the imaginary land of Shangri-La, for example, people are said to lead a charmed existence for a thousand years. The Spanish explorer Ponce de Leon was convinced that he would find the Foundation of Youth in what is now the state of Florida. According to the Bible, Methuselah lived to be more than 900 years old. The subject of longevity is fascinating, and scientists study individuals such as Jeanne Calment to learn about the aging process. Calment died in 1997 in Arles, France, at the age of 122. She never married, and she lived in her own apartment until moving to a retirement community when she was 109. Most scientists agree that bodies will last, at best, about 125 years. This potential has changed little since modern human beings appeared more than 100 thousand years age. Recent improvements in medicine and the environment have extended life expectancy, especially for those from poorer parts of the world. It is not clear, however, whether such improvements will lengthen life expectancy beyond a certain point. Life expectancy is the number of years an infant can be expected to live, given the conditions into which it is born. Life expectancy, therefore, is affected by nutrition, medical care, and social and political circumstances. An individual's genetic makeup is also an important factor. Children from long-lived families can hope to enjoy long lives themselves. According to recent data, the average life expectancy worldwide in 1998 was 67 years. This can be compared with an average life expectancy of 77 in the United States. In 1970 the average life expectancy worldwide was 61 years, or 6 years less than it was in 1998. This same period saw a drop in infant mortality --- the death of a child before the first birthday---from 80 births out of 1,000 to 54 births out of 1,000. According to some researchers, the rise in the average life expectancy is due primarily to the drop in infant mortality. It is not so much that adults are living to an older age. It is, rather, that more people are living into adulthood because more children are surviving beyond their first birthdays. Although it may be possible to improve the life expectancy of a particular group of people,   _   .
it is more difficult to affect the rate of infant mortality it is unlikely that one will be able to extend the potential life span of human beings in general the process of evolution is extending the potential life span beyond 125 years the potential that bodies will last, at best, about 125 years has changed much since modern human beings appeared