Female human body blocks weak sperm, scientists find

Reproductive tract's shape lets only strong swimmers through to egg, research suggests

For millions of sperm it is the end of the road. Scientists have found evidence that the female reproductive tract is shaped in such a way that stops poor swimmers from reaching their goal.

Researchers used small-scale models and computer simulations to show that pinch points that behave like gates along the sperm's arduous path from cervix to egg allow only the fastest ones through.