The phenomenal speeds reached by the teenage Chinese swimmer Ye Shiwen at the 2012 Olympics are raising questions about whether the gap between men and women in sport may one day disappear.
Ye, who has so far won two gold medals and broken a world record at the London Games, clocked a time for the last, freestyle lap of her medley swim that rivaled the male champions.
There's plenty of evidence to show the gender gap exists, and has done ever since women have competed alongside men in international sporting events.
Yet the gap has been narrowing over the decades - so will women one day catch the men?
They'll get close, says John Brewer, a professor of sports science at Britain's University of Bedfordshire - but only in some events.
More women doing more sports
Women first took part in the Olympic Games in Paris in 1900, four years after the first Games of the modern era in Athens.
Female participation has increased steadily since then, with women accounting for around 45 percent of athletes at the 2012 Games, compared with 23 percent in Los Angeles in 1984 and just over 13 percent in Tokyo in 1964.
But women have not always been allowed to compete in all the sports at all the distances that men tackle.
In more "mature" sports where women and men have been running, jumping or swimming alongside each other in international competition for many decades, the gap has stabilized, Brewer said.
"But where the gap is still narrowing is in female sports that are less mature, like the endurance events - the marathon, the 10,000m, and long-distance swimming," he said. Women have only been allowed to run the marathon at Olympic Games since 1984, while the 10,000 meter women's running race was only introduced in 1988.
A study published in 2010 in the Journal of Sports Science and Medicine, which looked at the difference between men's and women's world records since the start of the modern Olympics in 1896, found that the gap narrowed consistently until about 1983, then stabilized.
The average difference between men and women across all events is around 10 percent, but that ranges from 5.5 percent in the 800-meter freestyle swim to 18.8 percent in long jump.
Experts point to important physiological differences between men and women.
China's Ye Shiwen (R), with her gold medal, smiles with silver medal winner Elizabeth Beisel of the US during the women's 400m individual medley victory ceremony at the London 2012 Olympic Games at the Aquatics Centre July 28, 2012 (Photo: Reuters)
More fat, less muscle
"Females tend to have more body fat, which makes them more buoyant in the water, and that can sometimes help in terms of speed," said Alexis Colvin, assistant professor of orthopaedics at the Mount Sinai School of Medicine in New York.
"But on the flip side, women have less muscle mass and power, so the effect is cancelled out."
Men's hearts are generally larger, allowing them to pump more blood for each heartbeat, and their lungs are able to take in more oxygen for each breath. The combination means their blood can take more oxygen to the muscles, making them stronger and more powerful.
The relative infancy of some disciplines for women and the Olympics means, however, that women could squeeze the gap as coaches, sports scientists and psychologists learn more about how to train, support and push women at elite level.
With so many more years of data to study, the science behind training is likely to be skewed towards men, and learning more about how elite women competitors train, improve and compete could help coaches get more out of them.
"Even though biology is responsible for a lot of things, we're also learning a lot more about the most effective ways for women to train and recover," Colvin told Reuters. "That might help us overcome some of the biological differences."
Brewer thinks much of that women-specific knowledge has already been gained and implemented - something that could account for the rapid narrowing of the gender gap in some swimming and running events in recent years.
"But while a very good female be able to beat a good male, at the highest level the very best females won't be able to beat the very best males," he said. "Sadly, in my view, the gap will never close completely."