The video shows why some sperm will never be able to fertilize an egg

It has long been said that "strong swimmers" prevail, but new research shows how important it is to be fast in the race for fertilization. This is because zipped sperm will probably be the only ones fast enough to sneak past the bottlenecks of the female reproductive tract.

Scientists have used small-scale models and computer simulations to "study sperm locomotion" in research that may one day be used to improve male fertility. But meanwhile, he has produced a beautiful video of sperm that has trouble swimming upstream (say it five times quickly).

With a single ejaculate, 100 million sperm can go back into the female reproductive tract, but there are bottlenecks in the path from cervix to egg, called "stenosis". These can alter the flow of mucus and have an impact on how little guys are trying to fight the current.

Researchers at Cornell University have developed a fallopian imitator and have used human sperm and bull to test it and observe how small swimmers navigate these difficult choking bottlenecks.

They discovered that the sperms congregate under the opening of the throttling neck and that the fastest ones leading the pack are just facing each other, which gives them a better shot at the line of d & # 39; Arrival, while slower swimmers are caught in currents that disperse and propel them backwards.

"The accumulation below the stenosis occurs in a hierarchical manner, so that dense concentrations of sperm with higher velocities remain closer to the stenosis, with more dispersed networks of spermatozoa at a slow, late speed," wrote the researchers.

John Amory, professor and fertility expert at the University of Washington, who did not participate in the study, said this confirmed a key question regarding the characteristics of sperm gain.

"Clinically, we have always suspected that it was the very mobile sperm responsible for fertilization, and this paper suggests that this is the right way to look at things," he said. "It's a very cool little model."

The research was published this week in the journal Progress of science.