Age. Suresh Rattan

is a very interesting and true story about taking life expectancy at face value. A story with dire consequences. In 1955, Madame Calment had already lived ten years longer than the expected lifespan of French women at that time. Perhaps that is why, around that time, her attorney offered to buy her house through the French viager system.

      The viager system of buying and selling property follows a set of simple but somewhat peculiar rules. Basically, the seller agrees to sell the property at about 30% of its current market value. The seller then receives an agreed sum of money every month as an annuity or pension (the rente viagère) for rest of their life, along with retaining the right of usage (droit d’usage) over the property.

      The attorney, who was considering Madame Calment’s already advanced age of 80 and the reliability of the statistical predictions, thought he had made a wonderful bargain. As it turned out, the property deal turned into a 42-year-long financial nightmare. Both the attorney and his son ended up dying before Madame Calment did, and paying far more than the actual price of the house.

      FASTER THAN USAIN BOLT

      At a global level, the average life expectancy of human beings has been increasing steadily from less than 25 years in ancient times to about 71 years in 2016. This does not mean, however, that the average lifespan does not vary among countries and among different groups within a country.

      According to present-day statistics, Monaco is the country where people can expect to live the longest – 89.57 years – whereas in Chad the average life expectancy is just 49.44 years. We could also focus on men and women separately. For example, in Denmark, at present, men live an average of 76.68 years, while women live five years longer.

      A multitude of factors affect life expectancy, such as how many children die in the first five years of life; how many women die during childbirth; how many people die due to infectious and other diseases and due to natural and man-made catastrophes.

      The important question is, of course, whether this historic increase in lifespan will continue forever, or whether it has reached its maximum? Biologists and other scientists are divided into two groups on this question. One group holds the position that, considering the ongoing developments in health-care technology, life expectancy will continue to increase and will surpass 100 years within the next ten to fifteen years.

      The other group of scientists, especially biologists like myself, hold a different view. An increase in life expectancy cannot continue indefinitely, because soon we will face the realities and limitations of life’s biological processes.

      We can try to imagine what a never-ending improvement in, say, race results at the Olympic Games would imply. Over the past 100 years, the clock time spent on covering almost all distances has been decreasing. If, based on this fact, I assume that these shorter clock-times will continue into the future, then by the year 2200, all races will be completed as soon as the starting shot is fired.

      Obviously, this is absurd and nonsensical. Even the Jamaican sprinter Usain Bolt and the cartoon character Speedy Gonzales are not that fast. Sooner or later, we all have to face and accept the limits of our biology.

      Therefore, my fellow biogerontologists and I reckon that our average lifespan will stabilise at about 90 to 95 years. Even this limit is still a long way into the future. There are still too many social, political and economic factors that prevent everyone, around the world, from achieving such a ripe age.

      DARWIN KNOWS

      Biologists almost always agree that answers to ‘why’ and ‘how’ questions can be found in Charles Darwin’s theory of evolution. I think that Darwinian theory can also provide answers as to what lifespan we, as members of the human species, should expect to reach.

      Life on Earth was neither designed nor created in a few days. It started about 4 billion years ago. Initially, life was found only as single-celled life forms, such as bacteria, which had the entire planet to themselves. Multicellular life, such as algae, mushrooms and worms, evolved over the next billion years or so. Only over the last 570 million years did the kind of life forms we now share the planet with begin to emerge.

      This stage of evolution started with shrimps and insects, followed by fish about 530 million years ago. Land-based plants first appeared 475 million years ago. Mammals did not emerge until almost 300 million years later.

      Biologists reckon that there are currently 10–14 million species in existence. Millions of other life forms have already become extinct. We, the human race, with a quarter million years behind us, are the latest and youngest product of evolution. But we do not know how long we will survive, either as a species or as individuals.

      A species can only survive for millions of years if it is successful in reproducing its own kind, generation after generation. Species that have become extinct did so either because they could not reproduce in large numbers or because they were eliminated very rapidly by some natural catastrophe. The mass extinction of dinosaurs about 65 million years ago is thought to be the result of the impact of some comet, asteroid or meteor from outer space.

      You and I are alive today because our parents were able to produce children. As were their parents, and their parents, and their parents before them, all the way back to … some ancient ancestor we do not know.

      What we do know for sure is that successful reproduction and the continuation of generations is the ‘biological purpose’ of life. This is the purpose of life for a bacterium, an insect, a rat, my Kutta, me and you. It sounds somewhat depressing. We are humans, and we would like to believe that our purpose in life is some higher and nobler one to which we must aspire.

      We may or may not like it, but as a biological entity with the scientific name Homo sapiens, our purpose in life is exactly like that of all other biological entities. But evolving into ‘human beings’ from Homo sapiens seems to be a development unique to our species, which involves language, art, culture and societies.

      In any case, every species requires a certain duration of time to grow, develop and reproduce. We biogerontologists refer to this duration of the lifespan as the ‘essential lifespan’ of a species. Some other scientists also call it the ‘warranty period’ of a species. Essential lifespan is thus the age that enough individuals of a species must achieve in order to viably reproduce the species in the long term.

      Essential lifespan can be a few minutes for some bacteria, a few days for worms and flies, and months or years for other life forms. For us, Homo sapiens, the essential lifespan is about 40–45 years. From nature’s perspective, our species does not need more than 45 years to complete the process of growth, development, maturation and reproduction.

      There is nothing intrinsically good or bad about a given species having a short or long essential lifespan. The duration is just a reflection of how different species have evolved, and the time they need to continue to survive as a species.

      Is the end of the essential lifespan the right age to die then? Darwin would probably say so, and I would fully concur.