Fertility Today: Where Don't Babies Come From? - The Atlantic

Important fact: 

But human babies, compared with other mammals, are particularly helpless. Is there an evolutionary reason for this?
It’s because of our big brains. In most primates, a baby develops in a mother’s body until it has half of its brain size. A lot of brain growth occurs in the womb. At birth, human brains are a quarter of adult size. We can’t give birth to babies any later because the brain will just fit through the pelvis as it is. It takes about a year for us to get to the position where monkeys and apes are at birth. That makes human babies particularly dependent on care for their first year of life, which has implications for social organization. Special social support is necessary.


And why is our pelvis of this particular size and orientation?

So we can walk upright. 

So we sacrifice initial mobility and safety for the bigger brain and being able to walk on two legs -- arguably the two most important pieces of our evolutionary success. 

I heart science.