Women's bodies and medical needs are vastly different than men's way beyond their reproductive systems. Women wake sooner from anesthesia, have less familiar symptoms of cardiovascular disease and are more likely to suffer from depression and sleep problems-- just to name a few of the differences.

Adding another layer of competition to the mating game, scientists are reporting possible biochemical proof that the reproductive system of female mammals can “sense” the presence of sperm and react to it by changing the uterine environment.

A study led by researchers at UCL (University College London) demonstrates that female reproductive function is influenced by childhood environment. This suggests there is a critical window of time from about 0-8 years of age that determines the rate at which girls physically mature and how high their reproductive hormone levels reach as adults.