The past, present and future of uterine fibroids.

Human evolution -specifically the development of bipedalism- altered the shape of the pelvis so that legs alone provided locomotion across the ground. As a result, the forelimbs were freed from locomotion. Though speculative, hands freed from locomotion may have led to the expansion of hand tool use and brain enlargement. With a pelvis no longer optimised for childbirth and with larger fetal brains, childbirth became more challenging. An "obstetrical dilemma" was created. How could large-headed babies be pushed through a narrowed, convoluted pelvis? More uterine muscle, a "neomyometrium," evolved in the uterus, to increase the force of contractions. Because fibroids develop from myometrial tissue, additional fibroids came along with the neomyometrium. Until recently, the fibroid burden that accompanied bipedalism did not become apparent until the advent of modern contraception. Mendelian randomisation studies have demonstrated causal links between women's reproductive histories and their risk of developing fibroids. Multiparity and infrequent menstruation, universally common until only recently, kept this fibroid risk hidden until socio-demographic changes and hormonal contraception unmasked fibroids that evolved with the neomyometrium. Simple therapeutic approaches that (i) periodically and temporarily emulate the clot formation that occurs within the blood vessels of the uterus following childbirth and that (ii) reduce the number of lifetime menstrual cycles may be able to reduce the current high incidence of fibroids.