Mummy, why can't I live forever?

George, 8

You could start with some gentle comparisons to ease yourself into this scientific minefield - otherwise known as the evolution of ageing.

Begin in a general way with other examples in nature. “Well, George,” you could say. “Everything lives for a certain time, peaks and then fades. It's a pattern you see everywhere from plants to animals, even your pet goldfish. Human beings are only really designed to live long enough to look after their children and then make way for the next generation.”

If there's an insistent “But why?”, then it's time for a biology lesson. As Professor Ian Stuart-Hamilton, a specialist in the psychology of ageing, explains: “Our body is made up of cells and when they reach a certain age and can't duplicate themselves perfectly, they die off. If cells were immortal and could still duplicate even when they're damaged, it would be like photocopying a bad print over and over again.” All sorts of diseases, from muscle weakening to cancer, would then thrive.

But what if George asks why those cells have to decline in the first place? The simple answer is that no one can agree why all living things must die. Some argue that because nature is competitive and most animals die before old age - which explains why you never see geriatric animals running about in the wild - there simply hasn't been a biological need to keep the body healthy forever. Until now, which is why scientists are busily extending the lifespan of yeast fungus by altering their genetic make-up and believe that an 800-year lifespan is just one genome away.

Finally, you could ask George why immortality is such a great idea anyway. Presumably it would only really appeal to him if all his friends could live forever too.

“It's is an idea that raises yet more questions,” says Professor Felicia Huppert, director of the Well-being Institute at the University of Cambridge. “You could suggest that although it's wonderful doing things for the first time, wouldn't it become less interesting after you've done them several thousand times?”

Stewart-Hamilton agrees. “If we knew we had forever, we'd lose that great spark that drives us. Look at the Galapagos tortoises. They have an average life expectancy of more than 200 years. But they don't half lead boring lives. What, really, is the point?”

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