If it can hold up to 2029, says Ray Kurzweil, Google’s chief futurist, medical advances will start “adding a year every year to life expectancy. And with that I’m not talking about life expectancy at birth, I’m talking about Life expectancy in the remaining years.” Curious readers may wonder what this trend will do to global population growth, but I will limit myself to a brief review of the survival facts.
In 1850, life expectancy for men and women ranged around 40 years in the United States, Japan, and most of Europe. Since then, these values have seen an impressive almost perfect linear increase which has caused them to nearly double. Women live the longest in all societies, with the current maximum being 87 or more in Japan.
It is entirely possible that this trend will continue for a few more decades, considering that between 1950 and 2000, the life expectancy of elderly people in rich countries grew by about 34 days a year. But without the fundamental discoveries that are changing the way we age, the trend toward longer lives is sure to slow and eventually disappear. The long-term trajectory of Japanese women’s life expectancy — which rose from 81.91 years in 1990 to 87.26 years in 2017 — fits in a symmetric logistic curve already approaching the roughly 90-year convergence line. Tracks for other wealthy countries also give a rough estimate of the ceiling values. Available records of the twentieth century reveal two distinct periods of increased longevity: the spread of fast linear gains (about 20 years in a half century) until 1950, followed by slower gains.
If we are still far from the human life time limit, the largest survival gains should be recorded among the elderly, that is, those aged 80–85 should gain more time than those aged 70–75. This was in fact the case in studies conducted in France, Japan, the United States, and the United Kingdom since the 1970s and early 1990s, but since then, the gains have leveled off.
There may not be a specific limit genetically programmed over a lifetime – just as there is no genetic program that limits us to a specific running speed (see How Race Helped Chasing, p. 44). But age is a physical characteristic that results from the interaction of genes with the environment. The genes themselves can introduce biophysical limits, as can environmental influences such as smoking.
The world record for life is 122 years, which was claimed by Jeanne Calment, a French woman who died in 1997. Strangely enough, more than two decades later, Jeanne is still the oldest survivor ever, and by a large margin. (The margin is actually so large that it is questionable; the woman’s age and even her identity are questioned.) The second oldest major memory died at the age of 119 in 1999, and since then there have been no survivors beyond the year 117.
And if you think you have a chance of getting to 100 years because one of your ancestors lived that long, know that the estimated lifetime inheritance is modest, between 15% and 30%. Given that people tend to marry others like themselves – a phenomenon known as assortative mating – the true heritability of human longevity is probably lower.
Of course, as with all complex issues, there is always room for different interpretations of published statistical analyses. Kurzweil hopes that nutritional interventions and other tricks will extend his life until great scientific advances keep him forever. It is true that there are ideas about how to achieve this conservation, including achieving human cell regeneration by expanding their telomeres (nucleotide sequences at chromosome ends that degrade with age). If it works, you’d probably put the realistic cap above 125.
But for now, the best advice I can give everyone but a few remarkably early readers is to make plans for the future—though perhaps not for a future as distant as the twenty-first century.
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