There is good evidence to suggest that human lifespans in industrial societies will go on increasing.

Researchers at the University of California-Berkeley have examined the detailed records of deaths in Sweden from 1861 to the present day.

These are the longest and most accurate records of longevity ever compiled.

The team found that the maximum age that people live to in Sweden is steadily going up and shows no sign of levelling off.

The scientists say this brings into question the belief held by some that there is somehow a biological limit to longevity.

"We have shown that the maximum lifespan is changing. It is not a biological constant," said Professor John Wilmoth. "Whether or not this can go on indefinitely is difficult to say."

Although such reliable data as those recorded in Sweden are not available in other countries, Professor Wilmoth believes the findings of his team's analysis are applicable to populations in other industrialised nations.

Medical technology

In the 1860s, the oldest age in Sweden was about 100. In the 1960s, it was around 105. Today, it has gone up to about 108.

The UC-Berkeley team, writing in the journal Science, say that increased longevity can be due to numerous factors, including better sanitation and improved healthcare.

And they say that with continued improvements in these areas, particularly medical technology, there is every reason to suggest lifespans will continue to edge upwards past 110.

"Human progress is real, somehow," Professor Wilmoth said. "We are changing the limits of the human life span over time."

Many scientists believe there is a set limit to lifespan because the body's organs and tissue begin to wear out at a steady rate over time.

Much of the research into ageing aims to get a better understanding of the biological processes which trigger the steady deterioration in the cells that make up our bodies.

When Jeanne Calment of France died in 1997 at 122 years of age, she was acclaimed as the longest-lived person. But there are unverified accounts of people living even longer.