It isn't the most elegant of races.

In a study that attempts to elucidate one of the "central unsolved problems" in human reproduction what separates the tens of sperm cells that find an egg, from the millions of cells ejaculated? British researchers are reporting that sperm crawl, collide and crash head-on into the walls of the female reproductive tract in their frantic swim to the site of fertilization.

"Despite it being the thing that put all of us here, effectively, we still know almost nothing about how something so simple and key to life actually happens in the body," said Dr. Jackson Kirkman-Brown, a senior lecturer in reproductive sciences at the University of Birmingham in the U.K.

"Every time a woman gets or doesn't get pregnant, there is something going on where what to me is an incomprehensible number of sperm two hundred million get reduced to a countable amount, 10, maybe."

Popular wisdom holds that sperm follow each other in their swim through the female tract "rather like you or I might swim through a swimming pool," Kirkman-Brown said.

Instead, the researchers observed sperm travelling along walls, ceilings and particularly corners as they navigated the "narrow and convoluted channels" of the female tract, the team reports in the journal Proceedings of the National Academy of Sciences of the United States.

Sperm failing to get to the egg dooms fertility. "But equally some of the most common things in contraception are based on sperm motility," Kirkman-Brown said. Oral contraceptives the Pill work by thickening cervical mucous and stopping sperm from getting to the egg.

With ever more people undergoing fertility treatment and the pharmaceutical industry looking to develop new contraceptives, "There has been a lot more interest in sperm motility," he said.

To try to get a better handle on the "individual and group behaviours" that occur, the researchers watched sperm swimming not on slides or in petri dishes, but through tiny, hair-thin mini-mazes etched into silicone and barely visible to the naked eye.

The micro-channels were filled with fluid mimicking the viscosity of fluid within the female reproductive tract, giving sperm a more realistic environment. The mini mazes "have lots of different twists and turns, so we can see how sperm cope with swimming around these," Kirkman-Brown said.

More here:
The great sperm race? Study reveals chaotic reproductive journey