Life expectancy

Human life expectancy is a statistical measure of the estimate of the average remaining years of life at a given age. The most commonly used measure is life expectancy at birth. This can be defined in two ways. Cohort LEB is the mean length of life of a birth cohort and can be computed only for cohorts born so long ago that all their members have died. Period LEB is the mean length of life of a hypothetical cohort assumed to be exposed, from birth through death, to the mortality rates observed at a given year. National LEB figures reported by national agencies and international organizations for human populations are estimates of period LEB.
Human remains from the early Bronze Age indicate an LEB of 24. In 2019, world LEB was 73.3. A combination of high infant mortality and deaths in young adulthood from accidents, epidemics, plagues, wars, and childbirth, before modern medicine was widely available, significantly lowers LEB. For example, a society with a LEB of 40 would have relatively few people dying at exactly 40: most will die before 30 or after 55. In populations with high infant mortality rates, LEB is highly sensitive to the rate of death in the first few years of life. Because of this sensitivity, LEB can be grossly misinterpreted, leading to the belief that a population with a low LEB would have a small proportion of older people. A different measure, such as life expectancy at age 5, can be used to exclude the effect of infant mortality to provide a simple measure of overall mortality rates other than in early childhood. For instance, in a society with a life expectancy of 30, it may nevertheless be common to have a 40-year remaining timespan at age 5.
Aggregate population measures—such as the proportion of the population in various age groups—are also used alongside individual-based measures—such as formal life expectancy—when analyzing population structure and dynamics. Pre-modern societies had universally higher mortality rates and lower life expectancies at every age for both males and females.
Life expectancy, longevity, and maximum lifespan are not synonymous. Longevity refers to the relatively long lifespan of some members of a population. Maximum lifespan is the age at death for the longest-lived individual of a species. Mathematically, life expectancy is denoted and is the mean number of years of life remaining at a given age, with a particular mortality. Because life expectancy is an average, a particular person may die many years before or after the expected survival.
Life expectancy is also used in plant or animal ecology, and in life tables. The concept of life expectancy may also be used in the context of manufactured objects, though the related term shelf life is commonly used for consumer products, and the terms "mean time to breakdown" and "mean time between failures" are used in engineering.

History

The earliest documented work on life expectancy was done in the 1660s by John Graunt, Christiaan Huygens, and Lodewijck Huygens.

Human patterns

Maximum

for any human is that of French woman Jeanne Calment, who is verified as having lived to age 122 years, 164 days, between 21 February 1875 and 4 August 1997. This is referred to as the "maximum life span", which is the upper boundary of life, the maximum number of years any human is known to have lived. Although maximum life expectancy is around 125 years, genetic enhancements could allow humans to live for a maximum of 245 years, according to InsideTracker. According to a study by biologists Bryan G. Hughes and Siegfried Hekimi, there is no evidence for a limit on human lifespan. However, this view has been questioned on the basis of error patterns. A theoretical study shows that the maximum life expectancy at birth is limited by the human life characteristic value δ, which is around 104 years.

Variation over time

The following information is derived from the 1961 Encyclopædia Britannica and other sources, some with questionable accuracy. Unless otherwise stated, it represents estimates of the life expectancies of the world population as a whole. In many instances, life expectancy varied considerably according to class and gender.
Life expectancy at birth takes account of infant mortality and child mortality but not prenatal mortality.

Era	Life expectancy at birth in years	Notes
Paleolithic	22–33	With modern hunter-gatherer populations' estimated average life expectancy at birth of 33 years, life expectancy for the 60% reaching age 15 averages 39 remaining years.
Neolithic	20–33	Based on Early Neolithic data, life expectancy at age 15 would be 28–33 years.
Bronze Age and Iron Age	26	Based on Early and Middle Bronze Age data, life expectancy at age 15 would be 28–36 years.
Classical Greece	25–28	Based on Athens Agora and Corinth data, life expectancy at age 15 would be 37–41 years. Most Greeks and Romans died young. About half of all children died before adolescence. Those who survived to the age of 30 had a reasonable chance of reaching 50 or 60. The truly elderly, however, were rare. Because so many died in childhood, life expectancy at birth was probably between 20 and 30 years.
Ancient Rome	20–33	Data is lacking, but computer models provide the estimate. If a person survived to age 20, they could expect to live around 30 years more. Life expectancy was probably slightly longer for women than men. Life expectancy at age 1 reached 34–41 remaining years for the 67–75% surviving the first year. For the 55–65% surviving to age 5, remaining life expectancy reached around 40–45, while the ~50% reaching age 10 could expect another 40 years of life. Average remaining years fell to 33–39 at age 15; ~20 at age 40; 14–18 at age 50; ~10–12 at age 60; and ~6–7 at age 70.
Wang clan of China, 1st century AD – 1749	35	Life expectancy at age 1 reached 47 years for the 72% surviving the first year.
Early Middle Ages	30–35	A Gaulish boy surviving to age 20 might expect to live 25 more years, while a woman at age 20 could normally expect about 17 more years. Anyone who survived until 40 had a good chance of another 15 to 20 years.
Pre-Columbian Mesoamerica	20–40	Expectation of life at birth 13–36 years for various Pre-Columbian Mesoamerican cultures, most of the results lying in the range 24–32 years. Aztec life expectancy 41.2 years for men and 42.1 for women.
Late medieval English peerage	30–33	Around a third of infants died in their first year. Life expectancy at age 10 reached 32.2 remaining years, and for those who survived to 25, the remaining life expectancy was 23.3 years. Such estimates reflected the life expectancy of adult males from the higher ranks of English society in the Middle Ages, and were similar to that computed for monks of the Christ Church in Canterbury during the 15th century. At age 21, life expectancy of an aristocrat was an additional 43 years.
Early modern Britain	33–40	18th-century male life expectancy at birth was 34 years. Female expectation of remaining years at age 15 rose from ~33 years around the 15th-16th centuries to ~42 in the 18th century.
18th-century England	25–40	For most of the century it ranged from 35 to 40; but in the 1720s it dipped as low as 25. During the second half of the century it averaged 37, while for the elite it passed 40 and approached 50.
Pre-Champlain Canadian Maritimes	60	Samuel de Champlain wrote that in his visits to Mi'kmaq and Huron communities, he met people over 100 years old. Daniel Paul attributes the incredible lifespan in the region to low stress and a healthy diet of lean meats, diverse vegetables, and legumes.
18th-century Prussia	24.7	For males.
18th-century France	27.5–30	For males: 24.8 years in 1740–1749, 27.9 years in 1750–1759, 33.9 years in 1800–1809.
18th-century American colonies	28	Massachusetts colonists who reached the age of 50 could expect to live until 71, and those who were still alive at 60 could expect to reach 75.
Beginning of the 19th century	~29	At the beginning of the 19th century, no country in the world had a life expectancy at birth longer than 40 years, England, Belgium and the Netherlands came closest, each reaching 40 years by the 1840s. India's life expectancy is estimated at ~25 years, while Europe averaged ~33 years.
Early 19th-century England	40	Remaining years of life averaged ~45–47 for the 84% who survived the first year. Life expectancy fell to ~40 years at age 20, then ~20 years at age 50 and ~10 years at age 70. For a 15-year-old girl it was ~40–45. For the upper-class, LEB rose from ~45 to 50. Only half of the people born in the early 19th century made it past their 50th birthday. In contrast, 97% of the people born in 21st century England and Wales can expect to live longer than 50 years.
19th-century British India	25.4
19th-century world average	28.5–32	Over the course of the century: Europe rose from ~33 to 43, the Americas from ~35 to 41, Oceania ~35 to 48, Asia ~28, Africa 26. In 1820s France, LEB was ~38, and for the 80% that survived, it rose to ~47. For Moscow serfs, LEB was ~34, and for the 66% that survived, it rose to ~36. Western Europe in 1830 was ~33 years, while for the people of Hau-Lou in China, it was ~40. The LEB for a 10-year-old in Sweden rose from ~44 to ~54.
1900 world average	31–32	Around 48 years in Oceania, 43 in Europe, and 41 in the Americas. Around 47 in the U.S. and around 48 for 15-year-old girls in England.
1950 world average	45.7–48	Around 60 years in Europe, North America, Oceania, Japan, and parts of South America; but only 41 in Asia and 36 in Africa. Norway led with 72, while in Mali it was merely 26.
2019–2020 world average	72.6–73.2

English life expectancy at birth averaged about 36 years in the 17th and 18th centuries, one of the highest levels in the world although infant and child mortality remained higher than in later periods. Life expectancy was under 25 years in the early Colony of Virginia, and in seventeenth-century New England, about 40% died before reaching adulthood. During the Industrial Revolution, the life expectancy of children increased dramatically. Recorded deaths among children under the age of 5 years fell in London from 74.5% of the recorded births in 1730–49 to 31.8% in 1810–29, though this overstates mortality and its fall because of net immigration and incomplete registration. English life expectancy at birth reached 41 years in the 1840s, 43 in the 1870s and 46 in the 1890s, though infant mortality remained at around 150 per thousand throughout this period.
Public health measures are credited with much of the recent increase in life expectancy. During the 20th century, despite a brief drop due to the 1918 flu pandemic, the average lifespan in the United States increased by more than 30 years, of which 25 years can be attributed to advances in public health.