By Peter Weiss
Sperm cells prepare a lifetime for just one goal: the race to an unfertilized egg. Now there’s a microscale apparatus that pits the little wigglers against each other in a preliminary heat. By separating top swimmers from the rest, the itsy-bitsy racecourse may ultimately improve the odds for infertile couples.
![](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2003/06/2998.jpg?resize=128%2C150&ssl=1)
In many cases of infertility, the semen contains an insufficient percentage of normal, mobile sperm. Centrifuging and other existing means of separating the healthier sperm cells from the legions of listless ones typically net a low percentage of good swimmers and may even damage them.