Present trends in human life expectancy were established in an era in which little to nothing was being done to target the mechanisms of aging. As of fairly recently, this is changing. There is now a growing contingent of researchers, entrepreneurs, and clinicians attempting to treat aging as a medical condition. This introduces a shift from (a) trying - and largely failing - to address the symptoms of aging, to (b) trying to control the causes of aging. This will inevitably produce far greater gains in life expectancy than those achieved in the past, but the size and timing of those gains will be hard to predict.
This is worth thinking on, when reading papers such as the one I'll point out today, in which the authors project past trends into the future. Those past trends, a slow increase in life expectancy at birth, as well as remaining adult life expectancy at every age, year after year, will almost certainly not continue as-is. It will rather leap upward as the first rejuvenation therapies worthy of the name are widely deployed. But when and by how much will the numbers change?
It seems a fool's game to try to predict that outcome with any accuracy, but a great many of the world's institutions have come to depend upon good predictions of future life expectancy, perhaps lulled by the consistency of the trend to date. Consider the massive providers of life insurance, pensions, entitlement programs, and so forth, all of which calibrate their operations to a given level of mortality and survival in later life. There will thus be some upheaval attendant to the grand success of adding a few decades to the healthy human life span in the years ahead. A changing environment tends to shake out the dead wood from the competitive economic landscape. But at the end of the day, longer healthy life spans are always an economic good. More people will be productive for longer, with lower medical costs.
This article reviews some key strands of demographic research on past trends in human longevity and explores possible future trends in life expectancy at birth. Demographic data on age-specific mortality are used to estimate life expectancy, and validated data on exceptional life spans are used to study the maximum length of life. In the countries doing best each year, life expectancy started to increase around 1840 at a pace of almost 2.5 years per decade. This trend has continued until the present. Contrary to classical evolutionary theories of senescence and contrary to the predictions of many experts, the frontier of survival is advancing to higher ages. Furthermore, individual life spans are becoming more equal, reducing inequalities, with octogenarians and nonagenarians accounting for most deaths in countries with the highest life expectancy.
If the current pace of progress in life expectancy continues, most children born this millennium will celebrate their 100th birthday. Considerable uncertainty, however, clouds forecasts: Life expectancy and maximum life span might increase very little if at all, or longevity might rise much faster than in the past. Substantial progress has been made over the past three decades in deepening understanding of how long humans have lived and how long they might live. The social, economic, health, cultural, and political consequences of further increases in longevity are so significant that the development of more powerful methods of forecasting is a priority.