'Battle of the Sexes' view of infertility

TEL AVIV, Israel, Sept. 15 (UPI) -- An Israeli evolutionary biologist theorizes reproductive organs are now in an "arms race" that may explain some fertility problems.

Dr. Oren Hasson of Tel Aviv University links the evidence of high present-day infertility and a biomathematical model developed by colleague Lewis Stone to form the "Battle of the Sexes" theory -- the bodies of men and women become reproductive antagonists, not reproductive partners.

Hasson explains that over time, women's bodies have come to reward only the most competitive sperm with egg penetration and men have responded by over-producing aggressive sperm -- some that persist on entering the egg despite "do not disturb" signs. However, having more than one sperm enter, usually causes the egg to die.

"It's a delicate balance, and over time women's and men's bodies fine tune to each other. Sometimes, during the fine-tuning process, high rates of infertility can be seen," Hasson says in a statement.

"That's probably the reason for the very high rates of unexplained infertility in the last decades."

The findings are published in the journal Biological Reviews.