Biology of Humans 4th Edition by Judith Goodenough,Betty McGuire

Exercise 26

Apes have a fairly easy time giving birth, compared with humans. A female ape has a relatively large pelvis, and the small head of her infant passes easily through a roomy birth canal (the channel formed by the cervix, vagina, and vulva). Birth in humans is decidedly more difficult and risky. With its large head, the typical human fetus may spend hours making its way through a narrow birth canal. What trends in human evolution might have produced the tight squeeze of human birth?