The Guardian talks to researcher Tom Kirkwood: "We've known for some time that ageing is extremely variable; that everybody is different and that the differences of individuals' experience of ageing are greater than differences in earlier stages of life ... And why so variable? ... Because of the nature of the ageing process. I've been involved in this field for more than 35 years and when I entered it people fondly believed that ageing was programmed; that there was a mechanism inside our bodies that determined how long we would live. It was kind of written into our genes that we would die at a certain age. What we've been able to show is that the idea of this genetically programmed ageing makes no sense at all. There is no evidence. ... But, surely, genetic influences - a family susceptibility to cardiovascular problems, for instance - play a part in determining longevity? Only to a degree. [For example] a Danish study shows that such influences only explain about a quarter of the factors determining a lifespan. ... What we now know is that the genetic factors that influence your longevity are not genes that measure out the passage of time; the reason we age and die is because, as we live our lives, our bodies accumululate a great variety of small faults in the cells, and the molecules that make up the cells in our body - so ageing is driven by this accumulation of faults. The genes that influence longevity are those that influence how well the body copes with damage, how aggressive our repair mechanisms are; they're genes that regulate the house-keeping and maintenance and repair." All the more reason to focus research on the development of biotechnologies that can do a far better job of repair.