Thursday, October 20, 2016

Aging and longevity

Life span of several species.
Data from Science News, 7-13-2016
It is often said that aging has been favored by natural selection to facilitate the replacement of one generation by the next. According to Alex Kowald (University of Newcastle), this statement is nonsense. It is evident that natural selection would favor individuals aging less and able to reproduce longer. Peter Medawar, Nobel Prize in Physiology and Medicine (1960), said in 1951: Wild living beings do not live long enough for natural selection to act on genes that affect aging. Death overtakes them long before they are near their limit of longevity.
Each species of living beings seems to have a maximum longevity. In humans, according to appearances, this limit does not seem to go far above 110 years. The longest proven human longevity corresponds to Jeanne Louise Calment (a French woman), who died at age 122.5.
The fight against mortality in the twentieth century focused initially on decreasing mortality in the first years of life, with spectacular results. In the late twentieth century and early twenty-first, the best results have been achieved in the reduction of mortality in the elderly, but longevity does not appear to have increased. Notice the attached figure, which represents the percentage of people who would die at a certain age in the next year. For people between 20 and 40, tangible results have hardly been achieved, because their mortality has always been low. For people above 100, mortality increases rapidly. By 1900, about one out of every two centenarians died in one year; by 2013, the proportion is still one in three.
Mortality data for Spain by the National Statistics Institute
Everything indicates that the curve of mortality, which in 1900 resembled a U, will end up looking like an inverted L, with a very low rate for most of our lifetime, followed by a sharp rise towards 100% at an age around 110. If this happens, the yearly increase in life expectancy will be reduced to zero. According to UN data, this increase reached its peak in the US by 1975-80, but has since declined. Ray Kurzweil's prediction, announcing that we will achieve immortality in a few decades, when the increase in life expectancy exceeds one year per year, is unlikely to take place (see a previous article in this blog).
Although it has been possible to delay aging in mice, their life span hasn’t been prolonged beyond 5 or 6 years. Some gerontologists argue that aging and longevity may not be correlated:
If aging and longevity are linked, then treating aging could very well make people live longer, healthier lives. If they are separate phenomena, then people could forgo the cancer, heart disease and other ailments of aging, but they would still have limited life spans. (Science News, July 13, 2016)
If this were true, although we were able to delay our aging, our longevity would not necessarily increase. If so, humans would live until about 100, and then die around the same age.

Manuel Alfonseca

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