Study shows birth is a tight squeeze for chimpanzees, too

According to a new study, chimpanzees, like humans, must contend with a confined bony birth canal when giving birth. In humans, the problem is exacerbated by our unique form of upright walking, since this led to a twisting of the bony birth canal, while the fetal head grew larger. The obstetrical dilemma therefore evolved gradually over the course of primate evolution rather than suddenly in humans as originally argued.