After the onset of puberty, women develop wider hips than men so that their pelvis can allow the birth of large-brained babies, says a new study.
The researchers analyzed pelvic development from birth to old age and found that until puberty, male and female pelvises are similar in width.
With the onset of puberty, female sex hormone estrogen concentration reaches high levels, which are maintained until menopause, as a result of changes in hormone levels.
The results, published in the journal PNAS, showed that with the onset of puberty, the male pelvis remains on the same developmental trajectory, while the female pelvis develops in an entirely new direction, becoming wider and reaching its full width around the age of 25-30 years.
"This implies that the female body can modulate its pelvic dimensions 'on demand' and is not dependent on genetically fixed developmental programs," said lead study author Marcia Ponce de Leon from University of Zurich's Anthropological Institute in Switzerland.
But why does the female pelvis contract again with the onset of menopause?
The researchers assume that a narrow pelvis is better suited to stabilizing the pelvic floor and thus to withstanding the high pressures that are generated in the abdomen during bipedal walking.
As such, men and women become more similar from the age of 40 -- at least as far as their pelvises are concerned.