lifespans

Lifespan is the length of time an individual organism lives, from birth to death. In scientific contexts, lifespan is described using two related concepts: maximum lifespan, the greatest age observed in a species, and life expectancy, the average number of years a newborn is expected to live under current mortality conditions.

Life expectancy varies with sex, geography, and social conditions, and has risen dramatically for humans over the past century due to improvements in sanitation, vaccination, nutrition, and medical care. Maximum lifespans differ greatly across species; some organisms live for many decades or centuries, while others survive only days or weeks.

Determinants include genetics, environment, lifestyle, disease burden, and access to healthcare. Aging is a complex, multi-factor process involving cellular aging, DNA repair capacity, telomere dynamics, metabolism, and tissue maintenance. Mortality tends to rise with age, a pattern described by models such as the Gompertz law.

Representative long-lived species include the bowhead whale (estimated around 200 years or more), the Greenland shark (potentially several centuries), and various turtles that commonly reach a century or more. Some species show negligible senescence, while many short-lived organisms die after a brief life stage.

Humans have seen substantial gains in life expectancy, but healthy life expectancy—years lived in good health—remains shorter than total life expectancy in many populations. Differences reflect biology, behavior, environment, and access to health services.

In research, lifespan is studied through life tables and aging biology to understand aging, disease, and interventions that aim to extend both lifespan and healthspan.