It’s a bipedalism thing:
The relatively narrow human birth canal presumably evolved as a ‘compromise’ between its abilities for parturition, support of the inner organs, and upright walking. But not only the size of the birth canal, also its complex, ‘twisted’ shape is an evolutionary puzzle. Researchers now present new insights into why the human birth canal evolved to have this complex shape. They suggest that the longitudinally oval shape of the lower birth canal is beneficial for the stability of the pelvic floor muscles …
Traditionally, it has been assumed that the transverse dimension of the human pelvis is constrained by the efficiency of upright locomotion. “We argue that the transverse elongation of the pelvic inlet has evolved because of the limits on the front-to-back diameter in humans imposed by balancing upright posture, rather than by the efficiency of the bipedal locomotion,” says Philipp Mitteroecker, who was also involved in this study. A longitudinally deeper inlet would require greater pelvic tilt and lumbar lordosis, which would compromise spine health and the stability of upright posture. These different requirements of the pelvic inlet and outlet likely have led to the evolution of a twisted birth canal, requiring human babies to rotate during birth.
University of Vienna, “Why do humans possess a twisted birth canal?” at ScienceDaily
Should somebody tell Nathan Lents?
The paper is open access.
You may also wish to read: Does Nathan Lents, Author Of A “Bad Design” Book Really Teach Biology? A Doctor Looks At His Claims About The Human Sinuses
More on bipedality/bipedalism: Paleontologist: Humans walked on two legs from the beginning Carol Ward: It seems to be a behavior that was present in some of the earliest members of our branch of the family tree. It represented what was really the initial major adaptive change from any apelike creature that came before us.
Researchers: Supernova prompted humans to walk upright Funny, if bipedalism originated in a global catastrophe, that it never occurred to any other primate to resolve the problem by becoming fully bipedal. But keep thinking. Resist groupthink.
Bipedalsm: Regulatory area cent.com/intelligent-design/bipedalism-regulatory-area-missing-in-humans/” target=”another”>missing in humans
Researcher: To Understand Human Bipedalism, Stop Assuming “A Chimpanzee Starting Point”
Rough terrain caused humans to start walking upright
Early bipedalism walked no straight line
We’ve also heard that bipedalism developed so we could hit each other. Or carry infants. Or scarce resources. Or save energy. Or cool down. But mainly so we could have our hands free for whatever. (Saving eneregy and cooling down don’t really count here because lots of other methods would have worked; they just wouldn’t have freed the hands at the same time.)
See also “I’m Walkin’, Yes Indeed I’m Walkin’” But Not Because It’s Necessarily a Better Way to Get Around
Also, Design perspectives and the physiology of walking