An American born a century ago would have been expected to live, on average, just 54 years. Many children died young, and giving birth was one of the most dangerous things a woman would do. But thanks to vaccinations, antibiotics, sanitation and better maternal care, we are now much more likely to die in old age than in our youth. An infant born today should live to see a 78th birthday.
The easy gains against the grim reaper have been won. Now as people live to ever older ages, they confront two broad sets of forces that conspire to impose the ultimate human limit. First, each extra year we live means another year of accumulated damage to the body's cells and organs—damage that slower cellular-repair systems cannot quite fix. In addition, age is the biggest risk factor for common deadly ailments that researchers have been relatively powerless against, such as cancer, heart disease and Alzheimer's.