Life expectancy

thumb|300px|Life expectancy and healthy life expectancy in various countries of the world in 2019, according to [[World Health Organization|WHO]]

[[File:Life expectancy UN map gradient 2023.png|thumb|300px|Map of the life expectancy at birth in the world in 2023 (UN estimate, smooth palette)

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thumb|300px|Life expectancy at age 15 years 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 (e<sub>5</sub>), 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 <math>e_x</math> and is the mean number of years of life remaining at a given age <math>x</math>, 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 (also known as actuarial 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

The longest verified lifespan 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.

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! Era !! Life expectancy at birth in years !! Notes

|Paleolithic||style="text-align:center;"|22–33

|Neolithic||style="text-align:center;"|20–33||Based on Early Neolithic data, life expectancy at age 15 would be 28–33 years.

|Bronze Age and Iron Age||style="text-align:center;"|26||Based on Early and Middle Bronze Age data, life expectancy at age 15 would be 28–36 years.||style="text-align:center;"|25–28||Based on Athens Agora and Corinth data, life expectancy at age 15 would be 37–41 years.

|Ancient Rome||style="text-align:center;"|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

|Early Middle Ages (Europe, from the late 5th or early 6th century to the 10th century)|| style="text-align:center;" |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|| style="text-align:center;" |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||style="text-align:center;"|30–33

|Early modern Britain (16th – 18th century) 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||style="text-align:center;"|25–40|| For most of the century it ranged from 35 to 40; but in the 1720s it dipped as low as 25.

|Pre-Champlain Canadian Maritimes

|style="text-align:center;"|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||style="text-align:center;"|~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 (by which time they had been surpassed by Norway, Sweden and Denmark). India's life expectancy is estimated at ~25 years,

|Early 19th-century England||style="text-align:center;"|25.4||

|19th-century world average||style="text-align:center;"|31–32 |||