The pelvis in the human female is an example of perfectly decent mammalian design rendered problematic by evolution. There are two difficulties. One: because humans are bipedal, the birth canal is tilted. The baby does not drop down a true cylinder; instead, the baby must travel the rather sharp curve of the pelvis. As a result, human births are much more troublesome than those of other large mammals. Two: on account of our wonderfully large brains, human babies have huge heads, which compounds the problem of the tilted pelvis.
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