Gentlemen, DEFEND your swimmers

Human sperms are naturally slower swimmers compared to our monkey counterparts.

                                                    http://www.physorg.com/news109934150.html

And if you have a defect in the Defensin gene (DEFB126) , you have to try even harder to get your partner pregnant. The DEFB126 protein is found on the surface of sperms. It protects the sperm and helps it swim through the woman's cervical mucus to fertilise the egg.

Scientists found that:
- About half of all men carry one copy of the defective gene
- About a quarter of all men have two defective copies
- Sperms from men with two defective copies were 84% slower in swimming through the experimental “cervical mucus”. 
- Wives of men with two defective copies are 30% less likely to give birth

Prior to this study, male infertility causes were largely unknown. With knowledge gained from such a study, couples trying to conceive could undergo genetic testing to identify the underlying problem and choose a suitable assisted reproductive method. 

Here's the paper