Actually it can but it is a very in depth. There was a show on the channel TLC(The Learning Channel) in which it this was a part of the show. The studies found that some sperm are designed to be hostile to other sperm.
The show was The Human Animal and Desmond Morris was the one who did that show.
It goes along the lines that the male produces three types of sperm. The first we all know about and that is the type the fertilizes the egg,the second is what is called blocker sperm. Their job is seems it so essentially block the way of sperm that might come from another male. And then the last is known as killer sperm. They apparently swim around looking for and attacking any foriegn sperm. There is even research that men can control the amount of "killer sperm" they produce depending on what partner they are with.
You can either try to find the video series that this was discussed in or you can find the book. Both will give you more info on the subject.
[This message has been edited by Blastoff9600 (edited 11-10-2002).]
DS 13 yr
DS 8 yr (3+ yrs ttc)
TTC #3 since 01/02