Male long-distance runners are not only fitter than most - they may also find it easier to attract women, researchers say.
People who are better at running half marathons are likely to have been exposed to high levels of the sex hormone testosterone before birth, researchers from the University of Cambridge have found.
This means they not only have better cardiovascular efficiency but also a strong sex drive and high sperm count - suggesting they have historically been chosen by women as more desirable mates.
Dr Danny Longman, from the university's division of biological anthropology, said: "The observation that endurance running ability is connected to reproductive potential in men suggests that women in our hunter-gatherer past were able to observe running as a signal for a good breeding partner."
Pre-birth exposure to testosterone has previously been found to give men an evolutionary advantage.
The latest research focussed on half marathon competitors and found the faster runners also tended to also have longer ring fingers - a signal of hormone exposure in the womb.
Researchers say the finding suggests females may have selected mates for athletic endurance.
This may be because 'persistence hunting' - exhausting prey by tirelessly tracking it - was a vital way to get food.
The team analysed 542 runners at the 2013 Robin Hood half marathon in Nottingham by photocopying hands and taking run times and other key details just after runners crossed the line.
They found that the 10 per cent of men with the most masculine finger ratios were, on average, 24 minutes and 33 seconds faster than the 10 per cent of men with the least masculine digits.
Dr Longman said that while training and muscle strength were more important than hormone exposure in running performance, the size of the study meant the findings were "conclusive" evidence of a predisposition.
