I REGULARLY get invitations to subscribe to US health and longevity magazines. The advertising blurb accompanying a typical offer exclaims: "Three minutes a day to a 120 year lifespan".
You are advised to consume large amounts of vitamin and mineral dietary supplements during these vital daily minutes. You are also promised that this daily three minute munch will ensure robust health, including a vigorous sex life; you can literally become "the oldest swinger in town".
Such advertising, of course, prompts questions. Is the process of gradually declining vigour in old age, ending in death, inevitable? If so, is it nevertheless sensible to significantly extend human lifespan beyond the current limit?
Is death inevitable for humans? In so far as present knowledge goes, yes. For some simple organisms, things are different. In a certain sense, many single celled organisms neither age nor die. For example, an amoeba, in an optimum environment, grows, and, when it is ready, simply divides in two?
In turn, the progeny also grow and divide in two. In this way the first amoeba attains a certain kind of immortality - at no stage can you say it has passed away. On the other hand, more complicated biological organisms go through the cycle of birth, growth, senescence and death.
The death of the body seems to be as natural as birth. Death within a limited period after birth ensures turnover of the species and allows evolution by natural selection to proceed efficiently.
If on the other hand, organisms did not die, and continued to procreate, those species with no, or few, natural predators would quickly growing numbers and crowd out most other species.
Turnover is a basic characteristic of life. Whenever nature presents a face of apparent constancy, this invariably masks an underlying dynamic equilibrium. Thus, the molecules in our cells continually break down and are replaced. In many of our tissues, whole cells are continually dying and being replaced.
For example, every second, 2 1/2 million worn out red blood cells are removed from your circulation and broken down. At the whole population level, constant species numbers simply reflects a balance between the birth rate and the death rate.
Death is part of life.
Different animal species have different lifespans. A mayfly lives for a day; a spider lives for a year; a mouse lives for three; a squid for four; a squirrel for six. A human being can live for 120 years. Some tortoises can live for 150 years. Plants easily hold the record. A bristlecone pine can live for more than 4,000 years.
As a general rule, among mammals larger species live longer than smaller ones. This may be due in part to the slower metabolism of the larger animals.
The metabolic theory of ageing holds that small mammals tick faster, burn rapidly and live for a shorter time than large mammals, which live longer at a stately pace. To use a mechanical analogy, if you take two engines, and run one continuously fast and hot and the other one at a slower rate, the faster running engine will show a smoky exhaust and will burn itself out well before the slower running engine.
But there are exceptions to the simple rule that lifespan is proportional to rate of metabolism. For example, some birds with high metabolic rates live longer than mammals three times their size. Consequently there are several other theories of ageing.
The oldest holds that senescence results simply from wear and tear. Cells taken from old animals and examined under an electron microscope show wear in the "cogs and gears" compared to the cells from a young animal.
But the wear and tear theory doesn't explain everything either. In some Third World countries, where life is hard and medicine a luxury, death rates in infancy and youth are high, but once a person reaches mature adulthood life expectancy can be as good as in developed countries. There appears to be an inner biological clock which determines the rate at which we age, and sets a limit on our lifespan.
But it might be argued that, if we live long enough we will each develop a disease, e.g. heart disease, and this is what eventually ends most lifespans. In other words, if medicine could abolish disease, would people live indefinitely? I'm afraid not.
It appears that there is such a thing as a "natural death". One US study reported that 30 per cent of autopsies, carried out on people who were at least 85 when they died, could identify no cause of death. These people seemed to have died of simple old age.
To return to the analogy of the two motor cars. The heavily used car wears out and dies much faster than the lightly used car. But consider an alternative scenario in which the heavily used car is regularly subjected to comprehensive repairs and maintenance. This would obviously greatly extend its lifespan.
Living cells also have a repair mechanism whereby the essential genetic material that controls day to day activities in the cell is maintained in good working order. But the repair mechanism itself becomes less reliable as the organism ages, and this results in the gradual accumulation of genetic mistakes.
Eventually, it can be envisaged that the cumulative effects of genetic mistakes, mechanical wear and tear, and metabolic burn out, conspire to end the life of the organism.
Until recent times, most people everywhere died young. On average, ancient Romans lived no more than 20 or 30 years. Two centuries ago, the average person would hope to live to 40. Average life expectancy in Ireland today is 75 years.
One must distinguish between life expectancy and maximum lifespan. In ages past, average life expectancy was much lower because of uncontrollable disease, high infant mortality, and powerful psychological factors.
But I am not aware of any evidence that the maximum lifespan: attainable by humans in past ages, in those people fortunate enough to escape disease and to be equipped with robust psychological health, was less than presently attainable lifespans. Over the past 200 years, average life expectancy has been slowly rising towards a maximum lifespan, which is probably genetically determined and no greater than about 120 years.
FUTURE advances in molecular biology may make it possible to extend human lifespan. Much research effort is afoot, particularly in the US, aimed at slowing ageing. Supplementing the diet with large amounts of Vitamin E is widely promoted as a way to slow metabolic burn out.
It is extremely unlikely that it will ever become possible to broaden human lifespan indefinitely to achieve immortality. Even if this could be achieved, it is doubtful if it would be desirable either biologically, medically, ethically or psychologically.
In any event, there are several uncomplicated ways currently available to us to achieve at least a measure of immortality.
Firstly, if you are a religious or spiritual person you may have no problem at all with the concept of immortality, since you will believe that you have an immortal soul. But even if you are not you can still aspire to achieving a measure of immortality, either by having some of your characteristics transmitted to future generations through your descendants, or even by having a memory of your existence preserved as a result of making a major contribution during your lifetime.
But, of course, there will always be people who will feel like Woody Allen when he was asked: "Mr Allen, how would you like to achieve immortality?" He replied: "By living for ever".