The difference between the forms of the pelvis of men and women scientists have traditionally explained by the hypothesis of the obstetric dilemma: wider pelvis is necessary for childbirth, which have a relatively large volume of the head, however, bipedalism requires a narrow pelvis. Recently this hypothesis was challenged with the emergence of new scientific data, therefore, it remains unknown what factors influence sex differences.

Scientists have studied the development of pelvic bones, using computed tomography 275 men and women of various ages from infancy to 95 years. The results showed that from about 10 years, in early puberty, development of the pelvic bones in men and women begins to differ significantly. To 25 years of age formed a wide basin, well adapted for childbearing.

The period of greatest sexual dimorphism patterns of the pelvis is observed in 25-30 years and 40-45 years bones again begin to change, becoming more similar to male, with a subsequent reduction in the width of the birth canal. Scientists believe that the development of the pelvic bones due to hormonal changes in puberty and menopause, namely fluctuations in the level of estradiol.

Estradiol — female sex hormone produced by the ovaries, but small quantities are also produced by the adrenal cortex in men. Plays an important role in the regulation of the menstrual cycle in women and the formation of reproductive tissues and also affects other tissues of the human body, including bones.