Life span extension in humans is self-reinforcing: A general theory of longevity

This article proposes that longevity is not merely the result of an absence of mortality but a self-reinforcing and positively selected life-history trait in social species. It argues that a small increase in longevity is amplified as (1) reductions in mortality at young ages increase natural selection for mechanisms of maintenance and repair at all older ages as well as increasing the potential for intergenerational transfers; (2) intergenerational transfers of resources from old to young increase fitness (e.g., through improved health, skill, and competitive ability) of the young and thus favor the presence of older individuals in a population; and (3) the division of labor increases both efficiency and innovation at all levels, resulting in increased resources that can be reinvested. This theory is framed around the longevity-oriented question posed two decades ago by the gerontologist George Sacher, "Why do we live as long as we do?," rather than the more prevalent question today, "Why do we grow old?" The article describes the foundational principles and the main phases of a model for the evolution of longevity mediated through social organization, and applies the concept specifically to human populations.