As we just discussed, humanity's evolutionary ascension from quadruped to biped caused some problems. Heck, we can thank the stupid vertical misuse of our horizontal spines for everything from back pain to hemorrhoids. But it also made our birth canals smaller, requiring moms to push out the goods ahead of schedule.
Comparative biologists believe that human infants would stay in the womb longer if the escape path wasn't so narrow. This is why you'll often hear an infant's first three months of life referred to as "the fourth trimester." By all rights the little half-baked goblin should still be inside the womb, but we just had to start walking upright.