Since the gene, called DAF-16 in worms, is found in many animals and in humans, the finding could open up new ways to affect aging, immunity and resistance in humans, the scientists said.

We wanted to find out how normal aging is being governed by genes and what effect these genes have on other traits, such as immunity, said Robin May of the University of Birmingham, who led the study.

Populations across the world are aging at a staggering pace, posing potentially big challenges for health and social care systems. A study by Danish scientists last year found that half of babies born in the rich world today will live to celebrate their 100th birthdays.

Scientists are keen to find out how people age to try to develop drugs to help them stay healthier as their lives extend.

What we have found is that things like resistance and aging tend to go hand in hand, May said in an interview.

May's team compared longevity, stress resistance and immunity in four related species of worm. They also looked for differences in the activity of DAF-16 in each of the four species, and found that they were all quite distinct.

Importantly, the differences in DAF-16 corresponded to differences in longevity, stress resistance and immunity between the four species, with higher levels of DAF-16 activity correlating to longer life, increased resistance and better immunity against some infections.

May said DAF-16 was active in most cells in the body and was very similar to a group of human genes called FOXO genes, which scientists believe play a role in the aging process.

The fact that subtle differences in DAF-16 between species seem to have such an impact on aging and health is very interesting and may explain how differences in lifespan and related traits have arisen during evolution, May said.

The study was published in the Public Library of Sciences (PLoS) One journal.

In a commentary on the study, Professor Douglas Kell of the Biotechnology and Biological Sciences Research Council (BBSRC), which funded the work, said the findings would help scientists understand some of the mechanisms that determine how humans age.

It is very important to develop a good understanding of healthy aging if we are to appreciate what happens to an older person's physiology when they become unwell or experience difficulties with everyday tasks such as recalling memories or moving around, he wrote.