Horizons in the Evolution of Aging
by Thomas Flatt & Linda Partridge

Human life expectancy worldwide has increased dramatically. During the ~ 300,000 generations since the divergence from our most recent common ancestor with the great apes, lifespan evolved to double its previous value. In the last ~ 200 years there has been a further substantial increase, increase, on average about 2.5 years per decade, attributable to environmental changes, including improved food, water, hygiene, and living conditions, reduced impact of infectious disease with immunization and antibiotics, and improved medical care at all ages [2–5]. As a result, most people are now living long beyond the ages at which most would have been dead in the past. Natural selection has therefore not had an opportunity to maintain evolutionary fitness at older ages. Presumably as a consequence, advancing age is the major risk factor for diverse types of loss of function, and for highly prevalent chronic and killer diseases, including cancer, cardiovascular disease, and dementia.

Consequently, healthy life expectancy has not increased as much as has overall life expectancy, 𝗮𝗻𝗱 𝘁𝗵𝗲𝗿𝗲 𝗶𝘀 𝗮 𝗴𝗿𝗼𝘄𝗶𝗻𝗴 𝗽𝗲𝗿𝗶𝗼𝗱 𝗼𝗳 𝗹𝗮𝘁𝗲-𝗹𝗶𝗳𝗲 𝗺𝗼𝗿𝗯𝗶𝗱𝗶𝘁𝘆 𝗯𝗲𝗳𝗼𝗿𝗲 𝗱𝗲𝗮𝘁𝗵 (𝗪𝗛𝗢 𝗱𝗮𝘁𝗮 𝗼𝗻 𝗹𝗶𝗳𝗲 𝗲𝘅𝗽𝗲𝗰𝘁𝗮𝗻𝗰𝘆).

Many modern humans inhabit a very different environment from that in which their life history evolved, with both protection from many of its dangers, such as predators, infectious diseases, and harsh physical conditions, and freedom from the need to forage extensively to avoid starvation.

𝗛𝗼𝘄𝗲𝘃𝗲𝗿, 𝘁𝗵𝗲 𝗿𝗲𝗮𝗱𝘆 𝗮𝘃𝗮𝗶𝗹𝗮𝗯𝗶𝗹𝗶𝘁𝘆 𝗼𝗳 𝗰𝗮𝗹𝗼𝗿𝗶𝗲-𝗱𝗲𝗻𝘀𝗲 𝗳𝗼𝗼𝗱, 𝘁𝗼𝗴𝗲𝘁𝗵𝗲𝗿 𝘄𝗶𝘁𝗵 𝘁𝗵𝗲 𝗹𝗼𝘄 𝗿𝗲𝗾𝘂𝗶𝗿𝗲𝗺𝗲𝗻𝘁 𝗳𝗼𝗿 𝗽𝗵𝘆𝘀𝗶𝗰𝗮𝗹 𝗲𝘅𝗲𝗿𝗰𝗶𝘀𝗲, 𝗮𝗿𝗲 𝗿𝗲𝘀𝘂𝗹𝘁𝗶𝗻𝗴 𝗶𝗻 𝗮 𝘁𝗶𝗱𝗮𝗹 𝘄𝗮𝘃𝗲 𝗼𝗳 𝗺𝗲𝘁𝗮𝗯𝗼𝗹𝗶𝗰 𝗱𝗶𝘀𝗲𝗮𝘀𝗲 𝘁𝗵𝗮𝘁 𝗵𝗮𝘀 𝗮 𝗺𝗮𝗷𝗼𝗿 𝗶𝗺𝗽𝗮𝗰𝘁 𝗮𝘁 𝗮𝗹𝗹 𝗮𝗴𝗲𝘀, 𝗯𝘂𝘁 𝗽𝗮𝗿𝘁𝗶𝗰𝘂𝗹𝗮𝗿𝗹𝘆 𝗼𝗻 𝗱𝗲𝗮𝘁𝗵𝘀 𝗳𝗿𝗼𝗺 𝗰𝗮𝗿𝗱𝗶𝗼𝘃𝗮𝘀𝗰𝘂𝗹𝗮𝗿 𝗱𝗶𝘀𝗲𝗮𝘀𝗲 𝗹𝗮𝘁𝗲𝗿 𝗶𝗻 𝗹𝗶𝗳𝗲.

Modern humans therefore often have many features in common with laboratory model organisms, which also inhabit highly protected, calorie rich, and physically restricted environments.