A LONG， HEALTHY LIFE<br >AN INCREASINGLY COMMON<br >PHENOMENON<br > mericans are living longer， healthier lives<br > than ever before--those age 65 and older are<br > now iO times the number they were in 1900.<br >People in their fifties and sixties today often have par-<br >ents， aunts， and uncles who are still fit and energetic.<br >NEW DEMOGRAPHICS IN THE UNITED STATES<br >The proportion of people in the<br >oldest and youngest age groups is<br >undergoing a shift. For every per-<br >son over 65， there are now only 2<br >under 18. Just 10 years ago the ra-<br >tio was i elderly person to 3<br >youngsters. Even the number of<br >Americans who live to be 100--<br >currently about 36，000--has dou<br >bled since 1980 (see TheNew<br >Centenarians--A Growing and<br >Lively Group， p. 13).<br > Families in which four and<br >even five generations live to<br >know one another are no longer<br >the rarity they once were.<br >AVERAGE LIFE EXPECTANCY THROUGH HISTORY<br >The changes in human life expectancy are depicted below. Although<br >there were increases throughout recorded history， the greatest strides<br >came in the early 20th centu~ andpromise to continue into the 2isl<br >3000 s.c.<br >AVERAGE LIFE<br >18 YEARS<br >The Great Sphinx at Giza<br >was carved out of stone<br >more than 2，600years<br >before Christ by men when<br >life expectancy was only<br >20 Fears.<br >LIFE SPAN VS. LIFE<br >EXPECTANCY<br >Gerontologists， scientists who<br >study aging， distinguish between<br >life span and life expectancy. Life<br >span refers to the biological limit<br >of human life. the absolutely old-<br >be extended (pp.26-28).<br > Life expectancy is a person s<br >average length of life based on<br >statistical probability. A baby<br >%.<br ><br >King Tutankhamen<br > of ERppt， shown<br > harpooning from<br > a riverboat， was<br > born in 13 70 ~.c<br > and lived only<br > 18 years.<br ><br >