The word “longevity” is sometimes used as a synonym for “life expectancy” in demography. At NOMIX, the term longevity refers only to especially long-lived, and healthy, members of a population, whereas life expectancy is defined statistically as the average number of years remaining at a given age. Longevity is best thought of as meaning ‘typical length of life’.
Since most theories in this field, s.a. the disrepair accumulation theory of aging, postulate that the potential for longevity of an organism is positively correlated to its structural complexity, and we human beings belong to the most complex mammals, we are widely considered to have a naturally limited longevity due to aging, which results in a life expectancy of 80-85 years for millennials in developed countries.
The United Nations has made projections up to 2300, at which point it projects that life expectancies in most developed countries will be between 100 and 106 years and still rising, though more and more slowly than before. Gaps in life expectancy between rich and poor countries may well not exist in the future, due to the exchange of technology and the industrialization and development of poor countries, similarly to the way life expectancies between rich and poor countries have already been converging over the last 60 years as better medicine, technology, and living conditions became accessible to most people.
“The possible existence of a hard upper limit, a cap, on human lifetimes is hotly debated,” write Léo Belzile and coauthors in a paper to appear in Annual Review of Statistics and Its Application. “It is sustained and widespread interest in understanding the limit, if there is any, to the human lifespan.” Their own re-analysis of previously incorrectly analyzed data on extreme lifetimes indicates that any longevity cap would be at least 130 years and possibly exceed 180. And some datasets, the authors report, “put no limit on the human lifespan.” These analyses “suggest that the human lifespan lies well beyond any individual lifetime yet observed or that could be observed in the absence of major medical advances.”
However, recent increases in the rates of lifestyle diseases, such as obesity, diabetes, hypertension, and heart disease, may eventually slow or reverse this trend toward increasing life expectancy in the developed world.