Narrator: This is Science Today. A University of California study supports the theory that reproductive competition during the evolution of primate species occurred at the level of sperm cell motility. Bioengineer Michael Berns of the University of California, San Diego Jacobs School of Engineering and the Beckman Laser Institute at UC Irvine, says the significant point of their paper is that the data fits very precisely with what people have suggested ...

Berns: That you have high level of sperm competition in rhesus monkeys and chimps and a lower level of sperm competition in humans and in gorillas. We have the chimps at one end, which are promiscuous with many partners, whereas they have the gorillas at the other end where they're strictly monogamous and the humans fall somewhere in between, which really raises some interesting questions about the evolution of human beings and their mating habits - is there some historical reason for this?

Narrator: For Science Today, I'm Larissa Branin.