Why do humans possess a twisted birth canal? Extraordinary shape makes births more difficult, but gu…

In most women, the upper part, or inlet, of the birth canal has a round or transversely (left-to-right) oval shape, which is considered ideal for parturition, but it is unknown why the lower part of the birth canal has a pronounced longitudinally (front-to-back) oval shape. This twisted shape…

Click here to view the original article.