If ants and bees are any indicator of human function, mixed ejaculates will fight for the chance to fertilize an egg.
In a paper in the March 19th issue of Science, investigators from the University of Copenhagen report that in bees and ants, seminal fluids contain toxins the impede rival sperm in the female reproductive tract.
I am a gay male, and when friends hear that we want to have a child someday, some have suggested that we mix our sperm for fertilization of a willing female. I’ve always said that I thought it was impossible because I heard long ago that sperm from different ejaculates are toxic to each other. I’m not sure where I got this, and if anyone is aware of data on human sperm, I would certainly be interested in learning about it! However this paper in Science suggests that it may be impossible for two males to mix sperm, or at least if they did, there would be a final fight in the reproductive tract to see whose sperm would fertilize the egg.
This an interesting extension of male rivalry!