September 17, 2011

For most of human history, mortality was very high, with life expectancy between 20 and 40 in most societies. At that life expectancy, nearly half of all children born die before reaching age 5, and fewer than 1 in 10 people survive to age 65, with infectious diseases being the biggest killers of humans over the centuries. Over the past 200 years, and especially since the beginning of the 20th century, humans have made great progress in controlling mortality. A combination of factors, including improved nutrition; advances in science that led to vaccinations to prevent severe illness; antiseptics to prevent the spread of bacterial contamination; drug therapies to cure disease; environmental controls such as clean water supplies, sewerage, draining of swamps, improved housing, improved clothing; and the promotion of personal hygiene, all helped to push life expectancy to higher levels all over the world. This happened first in the now-developed countries, but spread quickly to the rest of the world after the end of World War II.

During the Roman Empire, life expectancy was estimated to be 22 years. In the Middle Ages, with some improvement of nutrition, life expectancy increased in Europe to more than 30 years. In the beginning of the 19th century, as a result of improved nutrition, housing, and sanitation due to increasing income, life expectancy in the United States and Europe reached approximately 40 years. Currently in the United States, the odds that a female baby will survive to age 65 are equal to 86%, based on a life expectancy of nearly 80 years. This means that nearly half of all women born will still be alive at age 85.

The process of declining mortality follows a generally predictable path that has come to be known as the epidemiological transition. The main features of the transition are the change from most deaths occurring early in life largely from infectious diseases, to most deaths occurring later in life largely from chronic diseases. As life expectancy increases, a greater fraction of babies born survive to older ages, and human longevity gets closer to the human life span.

Life span refers to the oldest age to which human beings can survive, which is approximately 120 years, based on the oldest authenticated age to which any human has ever lived. Longevity refers to the actual experience that people have in terms of survival. While life span is thought be largely determined by biological factors, longevity has both biological and social components. Longevity is usually measured by life expectancy, which is the statistically average length of life (or average age at death), and is greatly influenced by the society in which we live, the genetic characteristics with which we are born, and the lifestyle that we maintain.

Human beings still have little control over biological factors such as the strength of vital organs, predisposition to particular diseases, and metabolism rate. Regarding the social factors impacting longevity, there are three major categories: (a) the overall social and economic infrastructure, (b) a person’s place within a given society, and (c) a person’s lifestyle, regardless of his or her place in society. In general, the wealthier a country is, the better able it is to provide the kind of infrastructure that helps to maintain a lower risk of death for everyone living there. Within any particular society, those at the top of the socioeconomic scale are more likely to have access especially to health care resources, which increase the probability of survival from year to year. Nonetheless, no matter what your status in society might be, certain kinds of behaviors (such as smoking and abusing alcohol and drugs) increase the risk of death, while other kinds of behaviors (such as regular exercise and a moderate, healthy diet) will lower the risk of death.

The major causes of death are (a) diseases that can be transmitted from one person to another, such as malaria, measles, plague, smallpox, and recently HIV/AIDS; (b) degeneration of a body, including chronic diseases such as heart disease, cancer, cerebrovascular disease, chronic lung disease, diabetes mellitus, and chronic liver disease and cirrhosis; and (c) products of the social and economic environment, such as accidental deaths, murders, and suicides.

The “real” causes of death may not necessarily appear on a person’s death certificate. In 1993, two physicians, McGinnis and Foege, estimated the “real” or “actual” causes of death in the United States in 1990. Of the 2,148,000 people who died in the United States that year, they found that 400,000 died as a result of tobacco use, and 300,000 deaths were caused by dietary and physical activity patterns of the United States population. Alcohol misuse was the third real cause of death in the United States, followed by infectious diseases, and then toxic agents such as environmental pollutants, contaminants of food and water supplies, and components of commercial products. Finally, they found that firearms were responsible for 36,000 deaths.

There is, of course, still a considerable amount of variability in mortality in the world, despite the world average life expectancy early in the 21st century of 67 years (65 for males and 69 for women). For example, sub-Saharan African countries have life expectancy between 46 and 50 years. The next lowest life expectancy region is South Asia where it is between 58 and 64. The highest life expectancy is found in Japan, where a female baby can expect to live to age 85. Several European countries, including France and Switzerland, have a female life expectancy of 83.

We can also compare urban and rural differentials in mortality. For example, life expectancy in 1841 was 40 years for native English males and 42 for females, but in London it was 5 years less than that. The early differences regarding urban and rural mortality were due less to favorable conditions in the countryside, than to unfavorable conditions in the cities. Over time, medical advances and environmental improvements have benefited the urban populations more than the rural ones, leading to the current situation of better mortality conditions in urban areas. Differences in mortality by social status are among the most pervasive inequalities in modern society, and they are most noticeable in cities. So, if one is part of a family of low socioeconomic status, this may put him or her at greater risk of death. Data clearly suggest that the higher one’s position in society, the longer he or she is likely to live.

As with income, there is a marked decline in the risk of death as education increases. Race and ethnicity are also sources of differentials in mortality in the United States. Data from National Center for Health Statistics showed that in the United States in 1998, at every age up to 70, African American mortality rates are nearly double the rates for the white population. African Americans have higher risks of death from almost every major cause of death than do whites. Marital status also counts for differentials in mortality. Married people tend to live longer than unmarried people do, not only in the United States, but also in other countries.

Gender is also responsible for differentials in mortality. Women live longer than men do, and the gap has been widening until recently. In 1900, women in the United States could expect to live an average of 2 years longer than men in the United States. By 1975, the difference had peaked at 7.8 years, although since then the difference has dropped to 5.7 years. In general, the difference between male and female life expectancy can be an important clue to the status of women in society. Since the evidence points overwhelmingly to an inherent biological superiority of women over men with respect to mortality, any society in which women die at a higher rate, or close to the same rate, as men, is a society in which social customs and inequalities have trumped the biological tendencies. In many Asian societies, women have historically been the last to eat (even though they do most of the cooking), and are less likely to be cared for if sick. These symptoms of lower status are then reflected in higher than expected death rates.

Throughout history, and still today in many developing countries, high rates of pregnancy in a society not well covered by health care systems can lead to high levels of maternal mortality and infant mortality as well. The infant mortality rate (IMR) is the number of deaths of infants under 1 year of age per 1,000 live births in a given year. Included in the IMR are the neonatal mortality rate (calculated from deaths occurring in the first 4 weeks of life) and postneonatal mortality rate (from deaths in the remainder of the first year). Neonatal deaths are further subdivided into early (first week) and late (second, third, and fourth weeks). In prosperous countries, neonatal deaths account for about two thirds of infant mortalities, the majority being in the first week. The IMR is usually regarded more as a measure of social affluence than a measure of the quality of antenatal and/or obstetric care; the latter is more truly reflected in the perinatal mortality rate (the number of deaths after 24 weeks of gestation, including stillbirths, and during the first week of life per 1,000 total births).

As deaths increasingly are pushed to the later ages, the issue has arisen as to whether life span may increase or whether societies will experience a “rectangularization” of mortality. An increase in life span would mean that humans had discovered ways to keep alive beyond the age that any human has thus far lived. While this seems theoretically possible, science has a long way to go before this is likely to be accomplished. Instead, it seems more likely that deaths will become increasingly compressed into a few years late in life. This will lead to a rectangularization of the age curve, in which almost everybody stays alive until age 100 or beyond and then quickly begins to die.

SEE ALSO: Ethnicity, Life expectancy, Marital status, Maternal mortality, Morbidity, Socioeconomic status

Suggested Reading

  • Caldwell, J. (1986). Routes to low mortality in poor countries. Population and Development Review, 12, 171—220.
  • Hoyert, D. L., Arias, E., Simth, B. L., Murphy, S. L., & Kochanek, K. D. (2001). Deaths: Final data for 1999. National Vital Statistics Reports, 49(9).
  • Hummer, R. A., Rogers, R. G., Nam, C. B., & LeClere, F. B. (1999). Race/ethnicity, nativity, and U.S. adult mortality. Social Science Quarterly, 80, 136-153.
  • Kannisto, V., Lauritsen, J., Thatcher, A. R., & Vaupel, J. W. (1994). Reductions in mortality at advanced ages: Several decades of evidence from 27 countries. Population and Development Review, 20, 793-810.
  • McGinnis, J. M., & Foege, W. H. (1993). Actual causes of death in the United States. Journal of the American Medical Association, 270, 2207-2212.
  • United Nations Statistics Division. (2000). The world’s women: Trends and statistics. New York: Author.
  • Weeks, J. R. (2002). Population: Introduction to concepts and issues (8th ed.). Belmont, CA: Wadsworth Thomson Learning.
  • Wilmott, J. R., & Horiuchi, S. (1999). Rectangularization revisited: Variability of age at death within human populations. Demography, 36, 475-495.


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