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 rivalled 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.
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-metre women's running race was only introduced in 1988.
Experts point to important physiological differences between men and women.
"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 orthopedics 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.
