Sexiness of a long-distance runner
Male long-distance runners are not only fitter than most - they may also find it easier to attract women, researchers have said.
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 said.
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.
Persistence hunters may also have possessed other qualities, like intelligence and generosity , which women looked for in a mate.
Dr Longman said: "It was thought that a better hunter would have got more meat, and had a healthier - and larger - family as a consequence of providing more meat for his family.
"But hunter-gatherers may have used egalitarian systems with equal meat distribution as we see in remaining tribes today.
"I n which case more meat is not a factor, but the ability to get meat would signal underlying traits of athletic endurance, as well as intelligence - to track and outwit prey - and generosity - to contribute to tribal society. All traits you want passed on to your children."
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% of men with the most masculine finger ratios were, on average, 24 minutes and 33 seconds faster than the 10% of men with the least masculine digits.
The correlation was also found in women, but was much more pronounced in men.
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.
He added: "Humans are hopeless sprinters. Rabbits, for example, are much faster sprinters, despite being fat and round. But humans are fantastically efficient long-distance runners, comparable to wolves and wild coyotes.
"We sweat when most animals would overheat; our tendons and posture are designed to propel our next strides - there was likely a selective pressure for all these benefits during our evolution."
Persistence hunting is thought to have been one of the earliest forms of human hunting, evolving approximately two million years ago, and can still be found in parts of Africa and Mexico.
"Hunters will deliberately choose the hottest time of day to hunt, and chase and track an antelope or gnu over 30 to 40 kilometres (18 -25 miles) for four or five hours," Dr Longman said.
"The animal recovers less and less from its running until it collapses exhausted and is easy to kill.
"This may sound crazy, but when a hunter is relatively fit the amount of energy they expend is actually tiny compared to the energy benefits of an antelope-sized animal, for example."