Читать книгу Age - Suresh Rattan - Страница 7

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.