Why do we die?

Can genetics find a 'cure' for ageing and, therefore, dying, or will humans, like other organisms, always be at the mercy of nature? By Tim RadfordOrganisms grow old because nature doesn't need them any more. If the purpose of life is to procreate and replicate successfully - this is the logic of the so-called selfish gene theory - then it helps to stay healthy long enough to generate children and provide them with food. Immortality arrives with your offspring, and is only guaranteed when all your children also have children.

Different species place their bets on life's roulette wheel in different ways. If you're an oyster or a salmon or a fruit fly, the process is over quickly enough: lay a huge number of eggs somewhere safely and die. If you're a tigress or a dolphin, the process isn't so simple: you have to bear the young, rear them, provide food on a daily basis and guide them to maturity. If you are a human, you get a little bit of extra grace: you can be useful to your grandchildren, so there is some evolutionary pressure to stay alive that little bit longer. And then there's the bonus: being human, you have all the resources of society and technology to keep you safe from predators and healthy and active for just a bit longer.

But sooner or later, the biological clock begins to run down. Cells that had faithfully renewed themselves begin to fail. A heart that pounded away in perfect synchrony begins to run down after a couple of billion beats. Joints that withstood rugby, football, rock'n'roll and the gymnasium treadmill start to creak. Skin that bloomed in the spring sunshine begins to weather and flake in life's autumn. Brains shrink, spines curve, eyes begin to fail, hearing goes, organs become cancerous, bones begin to crumble and memory perishes.

Ageing seems inevitable but, for some scientists, it isn't obvious why this process is inexorable. Human chromosomes seem to arrive with their own lifespan timing devices called telomeres, but precisely why and how telomeres are linked to ageing is still not understood. There are genes that seem to to dictate survival rates in fruit flies, nematode worms and mice, and these genes almost certainly exist in humans, but what works in an insect or even another mammal may not be much help to a human anxious to hang around a bit longer. Even so, in the last half of the 20th century, life expectancies were increasing everywhere in the developed and developing world, wherever there was appropriate sanitation, nutrition, education and medical care; and small groups of scientists had begun to ask whether life could be extended indefinitely. Clues to survival A much larger group was prepared to ask a simpler question: could a healthy, active, enjoyable life be extended a bit longer? Quite how this can be done - in the individuals or in society as a whole - is not so easily answered, but epidemiological and biochemical research has begun to produce some clues to survival. These are, in no particular order: Be at the top. Research in Japan, the US and Britain has confirmed that social status is linked to health and lifespan. Top civil servants outlive their deputies. Oscar-winning film stars on average live four years longer than ordinary Hollywood actors. The same is true for queen bees, which live 10 times longer than worker bees. Be British. Better still, be Japanese. British people in the more comfortable echelons of society tend to have lower rates of diabetes, hypertension, heart disease, stroke, lung disease and cancer than their American counterparts, even though they spend less on healthcare. The Japanese, of course, do even better. Choose your ancestors carefully: There are genes that control ageing. Nobody knows exactly what they are or how they work, but you stand a much better chance of being a centenarian if you have a sibling who has made it to 100. Exceptional longevity runs in families. So it is part of inheritance. Eat wisely: Forget about superfoods, but watch what you eat. Rats, mice and other creatures with restricted calorie intakes survive longer than their sated siblings. What works for mice may not work for humans, but there is no doubt that overeating multiplies health hazards.