A blood test to determine how fast someone is ageing has been shown to work on a population of wild birds, offering support to claims the technique could accurately predict the natural life span of humans.
The research represents the first time the ageing test has been used successfully on animals living outside a laboratory.
The test measures the average length of tiny structures on the tips of chromosomes called telomeres, which are known to get shorter each time a cell divides during an organism's lifetime.
Telomeres are believed to act like internal clocks by providing a more accurate estimate of a person's true biological age. This has led some experts to suggest that telomere tests could be used to estimate how long people have left to live if they die of natural causes.
At least one company is offering a blood test in Britain for people interested in seeing how fast they are ageing based on their average telomere length.
Scientists have performed the tests on songbirds living in the Seychelles.
"We saw that telomere length is a better indicator of life expectancy than chronological age," said David Richardson, of the University of East Anglia.