There’s been a lot of news recently about dying — or, more exactly, about surviving. According to figures for 2006-08 just published by the Office for National Statistics, life expectancy at birth in the Royal Borough of Kensington and Chelsea, West London, has reached 84.3 years for males, 88.9 for females.

Even those numbers pale beside a recent prediction from Professor Kaare Christensen, of the University of Southern Denmark, and his colleagues that most babies born in developed countries after 2000 will live to see their 100th birthday.

The discrepancy between these forecasts is because life expectancy estimates normally factor in the current average rate of dying, whereas Christensen’s calculations assume that death rates will continue to decline as they have done in the past.

Life expectancy in the developed world has climbed steadily — at an average rate of almost six hours each day over the past 170 years. The regularity of this trend is surprising as very different factors have contributed at different times — better sanitation and food and cleaner water in the 19th century; vaccination and antibiotics in the first half of the 20th.

In 1825, British mathematician Benjamin Gompertz suggested that the inherent chance of dying increases with age, doubling with roughly every eight years of life. Later, William Makeham, an actuary, pointed out that risks from outside events — such as those posed by road accidents and infections — do not change much with age. The combination of Gompertz’s and Makeham’s ideas did a pretty good job of predicting the pattern of human mortality over the middle years of life, and improvements in life expectancy were explained mainly by a decrease in Makeham’s “external” risks up to the 1950s.

But since then there have been some odd developments. The gain in life expectancy has continued, though it has come mainly from better medical care and disease prevention, with older people benefiting the most. And as people live longer, a paradoxical inaccuracy in Gompertz’s law has appeared. Death rates among the elderly aren’t increasing as fast as Gompertz said they should.

Although the adverts don’t say it, life insurance and pension companies survive by trying to make accurate predictions of when their customers will die. Their past models were based on the work of Gompertz and Makeham, and on the assumption that the future will mirror history. But current trends and the rising power of biology are making actuaries worry about immortality.

Mayflies live for a few hours, bristlecone pines for thousands of years. Methuselah aside, maximum human lifespan has remained at 100-120 years throughout history: the world record for longevity was set by Frenchwoman, Jeanne Calment, who lived for 122 years, 164 days. But certain fish, reptiles and sea anemones show “negligible senescence”: they repair themselves continuously and don’t usually die unless something kills them. So could humans live for ever?

The biology of ageing is a fascinating, complex area of science, advancing rapidly but riddled with controversy. One view is that animals are genetically programmed to die. This idea went out of fashion but is now back in favour, partly because mutations of certain genes in humans are known to cause dramatic premature ageing. An alternative view is that ageing happens because evolution does not select against genetic characteristics that disadvantage older animals. This is because certain genes that have damaging effects in later life do play a useful part in early development or in regulating reproduction.

Then there is the “disposable soma” theory of Professor Tom Kirkwood at Newcastle University. He suggested that the energy requirements of sexual reproduction compete with the need to maintain and repair the rest of the body, which is ultimately expendable — hence ageing.

Where most biologists agree is that the tendency for older animals to run out of steam has to do with their genes. Could genetic engineering fight the Grim Reaper? For yeast, fruit flies and mice, the answer is certainly “yes”. Blocking or activating certain genes (including one that glories in the name Sonic Hedgehog) can extend lifespan by 50 per cent or more. Some of these genetic effects are additive — tweaking two genes can prolong life more than tinkering with just one.

There is also the matter of what we eat. Low-calorie diets prolong life in many species, for reasons that aren’t entirely clear. And then there is resveratrol, a compound found in red wine, which extends lifespan by more than 20 per cent in mice and by as much as 60 per cent in fruit flies and fish. Not surprisingly, the drug companies are interested.

Here is an area of science that challenges our most fundamental concepts of human existence. The entire structure of society is organised around the rhythm of individual life — infancy, childhood, adolescence, working age, parenting, retirement, grandparenting and death.

The repercussions of the likely continuing increase in longevity will resonate through every aspect of our lives. The impact on the cost of healthcare and social services will depend on how well we can deal with the wear and tear of old age, especially on the brain. And if the demographic shift continues, there will have to be radical changes in career structures, salary patterns, retirement and pensions.

From 1925, when the UK state pension age for men was set at 65, until 1980, the remaining life expectancy for a 65-year-old male held steady at about 12 more years. But since 1980 it has increased by 2.4 months per annum — that means six extra years of state pension per man, on average. George Osborne’s apparently dramatic plan to raise the state pension age for men to 66 in 2016 still falls far short as a response to the relentless increase in longevity.

We need to think now about the consequences of defying death — even the miraculous but disastrous possibility that we might be able to live for ever.

Colin Blakemore is Professor of Neuroscience at the Universities of Oxford and Warwick. He is also a Fellow of the Royal Society and the former chief executive of the Medical Research Council

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