The quest for eternal life is as old as humanity itself. “Grant us liberation from death for the sake of immortality, as the cucumber is severed from its bondage to the creeper”, runs one of the ancient Hindu prayers in the Mahamrityunjay, or the “great death-conquering” mantra. Death is the ultimate end, mysterious and terrible, against which even the strongest is powerless.

How to conquer death is a question every civilisation has tried to address. Myths have grown around immortal beings like gods in every culture, and of valiant but futile attempts of mortal men to attain immortality. But science may be closer to finding an answer to this ancient quest now more than ever before. In the early history of life, unicellular organisms like prokaryotes, protozoans and algae had ageless bodies and were immortal.

The advent of sexual reproduction boosted our chances of survival manifold. It also brought about ageing and death about a billion years ago. But Nature provides examples of immortality: a bacteria does not die naturally unless killed by an antibiotic or UV ray, strawberry plants clone themselves, and the tiny hydrozoans regenerate themselves to defy ageing and death. Cancer cells are also potentially immortal. But first let us be clear about the concept of immortality, which means defying death in order to live forever. But actually, what is ‘forever’? Around 1900, the average life expectancy in the world was only 31 years.

At independence in 1947, Indians were expected to live only 32 years, today it is 69. This is not quite an eternity, neither is the Japanese life expectancy of 85 years. But if human lifespan can be increased to, say, 150 or 200 years, that would be almost like attaining immortality. So it is not death, but the span of life that is important and the secret to immortality may lie in slowing down our ageing process somehow. Nature again provides many such examples.

Blue whales live for 200 years and Greenland sharks for 272 years. The age of sharks can be measured by the number of layers in their eye tissues, and one has been found as old 512 years. In the Arctic seas in winter, fish and frogs are frozen solid when the sea turns into ice. They revive to life with the onset of spring when the ice thaws, emerging with vigour out of their extended wintry hibernation.

Usually when our body temperature is lowered, ice crystals begins to form and grow within cells, eventually rupturing the cell walls and causing death. Bur for fish and frogs, their blood flows as fluid even when they are frozen, because their blood glucose, which acts as anti-freeze, lowers the freezing point of blood which remains liquid and drives their body functions.

For humans, however, that kind of glucose concentration in blood will be too toxic for life. Scientists have tried different anti-freeze chemicals, but have not succeeded in freezing solid any human. Even if this becomes possible someday, it is not known if the mind of such a ‘defrozen’ human would retain its memory and all other traits, or would simply be a blank slate. Another way to immortality could be to preserve our identity, including complete memory and personality, in some other physical or digital avatar, even when our bodies die their usual physical death.

Cloning humans and transferring the memory of an old person to a freshly cloned newborn could be one way of preserving the identity through time.However, let alone humans, even no primate has been successfully cloned so far, and the technology for memory transfer lies only in the realm of wishful thinking. As regards slowing down or even stopping the ageing process, however, the scenario is not so dismal.

Improvement in sanitation and medicine had increased the average lifespan by almost 25 years since the 1950s, and as scientists probe deeper and deeper into the secrets of the ageing process, the hope for increasing our lifespan indefinitely remains no longer in the realm of science fiction only. Why do we age? There are many theories of ageing. Biologically, ageing is believed to be caused by the accumulation of a wide variety of molecular and cellular damage over time, leading to a gradual decrease in physical and mental capacity, increasing the risk of diseases and ultimately death.

The free radical theory of ageing proposed by Denham Harman more than 60 years ago postulates that ageing results from the accumulation of damage caused by free radicals, which are unstable oxygen molecules produced as the byproduct of the normal cell function. Ageing may also arise from “cellular senescence” when cells within an organism cease to divide. Oxidation of DNA within cells may accumulate errors and damage cells, causing the failure of cell division.

Then there are mitochondria ~ specialised structures within cells where sugars are oxidized to produce energy, and the process produces highly reactive molecules called reactive oxygen species (ROS) that damage the mitochondrial- DNA. An alternative theory is the “programmed ageing concept”, which holds that ageing is a genetically-programmed, a natural and irreversible process of deterioration over time, eventually leading to death.

There are three major factors behind the slowing or reversal of ageing ~ calorie restriction, telomerase and age genes. Experiments have shown that for worms, insects, rats, dogs and cats, 30 per cent less calorie intake increases the average lifespan by as much. Animals are programmed by evolution to survive on the minimum diet, as they are not always expected to find ample food. They can live in a state of near hibernation to prolong their lifespan by conserving energy.

But calorie restriction has been seen to make the animals lethargic and disinterested in life, and no human has been tested as yet for this. Quite obviously, it will affect the quality of life. Within the cell nucleus, our genes are arranged along twisted, double-stranded molecules of DNA called chromosomes. Every time a cell divides, the tips of chromosomes called “telomeres” get shortened and after 50- 60 divisions they practically disappear.

Then the chromosomes start falling apart and the cell stops functioning correctly, exhibiting signs of ageing. Leonard Hayflick in 1961 showed that normal human cells cannot divide after about 50-60 cell divisions, a limit known as the Hayflick Limit which is fundamental to ageing. The enzyme telomerase elongates the telomers and thus prevents them from shortening; when washed with telomerase, skin cells continue to divide far beyond the Hayflick limit, making these cells effectively immortal.

Even cancer cells use telomerase to proliferate without limit, and hence it requires caution to avoid the unwanted byproduct of cancer while trying to evade death. Genetic remedies are based on the fixing and repairing of damage caused to the DNA. The promising candidates in this area are gene FOXO3, Human Growth Hormone (HGH) etc., though studies remain inconclusive. The chemical resveratrol found in red wine has been found to activate an enzyme called sirtunin which apparently slows down the DNAoxidation process, and hence, ageing.

Besides biological immortality, there is also the possibility of digital immortality. The Human Connectome Project launched in 2010 aimed at mapping the entire human brain and to build its “network map” (connectome) to connect its structure to function and behaviour. Once the neural structure of the brain is completely deciphered, the mind can be uploaded into a computer that could control a robot that replicates a human in every respect.

Our consciousness can then be dissociated from the physical state of the body which will become redundant. While the mind remains trapped permanently inside the computer, its robot connectome will be free to explore the galaxies and experience its sights and sounds, heat and dust.But death is the natural end to life, and living without death may not, after all, appeal to all.

In an overpopulated earth, the race for natural resources like water may spark wars and catastrophe. As it is, the world population is projected to exceed 11 billion by 2100, and if we fail to stabilise the population, we might be forced to colonise another planet or risk assured mutual destruction of humanity. The gift of immortality may actually prove to be a curse.

(The writer is a commentator. Opinions are personal)