Mortality

During the twentieth century, humanity witnessed the most dramatic declines in death rates and increases in life expectancy at birth than at any other time in history. Based on prevailing death rates in 1900, male and female babies born at that time were expected to live to 46.4 and 49.0 years, respectively. Now that the twentieth century has passed, it is known that babies born in the United States in 1900 fared a little better than predicted at the time because of unanticipated declines in death rates that occurred at every age throughout the century. There were three main forces that led to these declines in mortality. The first, which occurred early in the century, was a rapid decline in the risk of death among infants and children. The combination of improved sanitation, refrigeration, the more widespread use and distribution of clean drinking water, and the development of controlled indoor living and working environments led to rapid declines in the risk of waterborne and airborne infectious and parasitic diseases (IPDs). Infants and children benefitted the most from these developments because their immature immune systems placed them at a higher risk of death from IPDs. Examples of some of the IPDs that waned early in the twentieth century include diphtheria, tuberculosis, smallpox, and cholera. The second force that led to declining death rates was the more widespread use of hospitals for childbirth, which contributed to declines in both maternal and infant mortality. The third factor was the introduction of antibiotics in the middle of the century, which has saved people of all ages from a wide range of bacterial infectious diseases. The fourth factor, which led to declining death rates at middle and older ages in the latter third of the twentieth century, occurred as a combination of improved lifestyles, advances in surgical procedures, the development of pharmaceuticals, and a host of other advances in the biomedical sciences. In this case, death rates from such chronic degenerative diseases as heart disease and some cancers were observed to have declined during this period. As evidence for the magnitude of the changes in mortality that occurred throughout the twentieth century, consider the fact that life expectancy at birth rose by thirty years during this time, which was an increase of magnitude and speed that exceeded that observed during the previous 100,000 years.

There is considerable speculation among scientists about the future of human longevity. Some believe that medical progress will continue into the future at a pace that is even faster than the remarkable gains made in recent decades. Such advances will certainly include new surgical procedures and pharmaceuticals to combat the consequences of aging-related diseases, but advances are also expected in genetic engineering and in research involving embryonic stem cells. Even more speculative, but certainly within the realm of possibility, are longevity gains that could arise from efforts to combat the aging process itself. Although there is reason to be optimistic that death rates will continue to decline in the future, some scientists have demonstrated that the rise in life expectancy will probably be much slower in the twenty-first century than it was during the twentieth century. This is because it is far more difficult to add decades to the lives of people who have already lived seventy years or more than it was, early in the twentieth century, to add decades to the lives of children saved from dying of infectious diseases. However, under any condition, humanity is embarking on a fascinating new journey into the science of aging that will undoubtedly change modern notions about aging and death.