Compared to most other animals, human babies are born more helpless and dependent on those around them (for example, most other species have young that are able

Compared to most other animals, human babies are born more helpless and dependent on those around them (for example, most other species have young that are able to crawl or walk already). I believe the theory I've heard goes something like: It was beneficial for humans to start walking upright, but that development puts selective pressure on having a narrower pelvis for increased stability. Having a narrower pelvis implies having a smaller birth canal, which in turn puts pressure on having a shorter gestation period.