The Human Body and Who We Are

As a species, we evolved walking across the savannah. Tens of miles a day. So our body is optimized for walking - a human being is the fastest land animal on the planet over very long distances. Partly because we don't have to stop and chew our cud. Although many of us do, in point of fact.
On the other hand, our heads have evolved to be large enough to hold very large brains.
These two facts form the razor's edge of our evolutionary development. The hips of human females must be narrow enough to walk long distances but wide enough to give birth to big-headed babies.
This makes birthing in our species uniquely difficult.
Also, if you compare the timing of the major events in the life span of humans with that for other primates, everything is proportional. Except birth. If we spent the same proportion of our lives in the womb as other primates do, we would be born 15 months after conception, not 9. So in a sense, all humans are born 6 months premature.