These days it is believed that approximately 10% of couples actively trying to conceive a child experience fertility difficulties. Some blame the increase of pollution in the world environment while others point to stress as a major contributing factor. However a researcher from Israel has a completely different take on the cause of infertility. According to Dr Oren Hasson, who is an evolutionary biologist at the University of Tel Aviv, the reproductive organs of the two sexes are involved in a kind of “evolutionary war” which Dr Hasson says is far from over.

According to Hasson the increase in the rate of infertility does not add up on from an evolutionary point of view. “By now, evolution should have improved our reproductive success rate. Something else is going on.” he said.

He set to work out more about the issue with the assistance of Prof. Lewi Stone, also from The University of Tel Aviv, working in the Biomathematics Division. Together they combined mathematical models with empirical evidence and came up with some very interesting conclusions.

They concluded that over thousands of years women’s’ bodies have forced male sperm to become “more competitive” with the “super swimmers” being awarded the prize of fertilizing the egg. As a reaction the male half of the population is now over producing the amount of these more aggressive sperm in order to increase the chances of successful fertilization.

But says Dr Hasson these changes serve to demonstrate the Law of Unintended Consequences as well. Those unintended consequences may have a lot to do with timing. When the “winning” sperm enters an egg it usually triggers a biochemical response to prevent other sperm from following it inside, which would kill the egg. It may now be though that even though this biochemical shield takes just minutes to deploy that some of these “super sperm” are breaking into the egg, terminating the whole process before it ever really began.

But according to this research the difficulties don’t end there. Women’s bodies have naturally begun developing defenses to this condition which is commonly known as “polyspermy” To avoid the potential death of a fertilized egg the female reproductive organs have changed, now forming a formidable barrier to most sperm. According to Dr Hasson “They eject, dilute, divert and kill spermatozoa so that only about a single spermatozoon gets into the vicinity of a viable egg at the right time.”

In simpler terms in response to any changes in the efficiency of male sperm is responded to by the female body in an apparently defensive manner. “This fuels the ‘arms race’ between the sexes and leads to the evolutionary cycle going on right now in the entire animal world.” The report concludes.

The reports entire findings were published in the Journal Biological Reviews.