London: Since the turn of the century, one of the standing puzzles has been how human fertilisation actually takes place.
Now, British scientists claim to have finally solved the puzzle -- sperms have an appalling sense of direction, crashing into walls and each other in the race to reach the egg, the `Daily Mail` reported.
On an average, a man releases 300 to 500 million sperm during sex with his female partner, but usually only one sperm enters into her egg.
In their study, the scientists from the University of Warwick and University of Birmingham have found that sperms avoid the "middle lane" of the female reproductive tract and instead crawl along the channel walls.
The sperms also struggle to turn sharp corners and crash into the walls and each other in a scene reminiscent of a demolition derby, say the scientists.
Lead scientist Dr Peter Denissenko from Warwick said: "I couldn`t resist a laugh the first time I saw sperm cells persistently swerving on tight turns and crashing head-on into the opposite wall."
The successful sperms were those that were best able to negotiate the complex and convoluted channels filled with viscous fluids, the scientists claim.
Dr Jackson Kirman-Brown from Birmingham said: "In basic terms -- how do we find the `Usain Bolt` among the millions of sperms in an ejaculate.
Through research like this we are learning how the good sperm navigate by sending them through mini-mazes."
In their research, the scientists injected sperm cells into hair-thin microchannels to study how they behaved in confined spaces. They found sharp turns in the channel caused `frequent collisions` as most sperm failed to turn in time.
Dr Kirman-Brown added: "Previous research from the group indicates that the shape of the sperm head can subtly affect how the sperm swim. Combined with this data we believe new methods of selecting sperm... May become possible."