Why does it take so long for us?
In: 3
Because we’re smart! And because we walk upright.
So somewhere down the evolutionary line that led to us (big smart apes), it was determined that walking upright 100% of the time is pretty neat. We spend less energy moving around, and we can have very specialized hands that are good for holding tools (but very bad for walking on), we can travel long distances, etc. Walking upright, however, requires very narrow hips compared to walking on all fours. It also requires some very strong booty and thigh muscles to keep us standing. This is problem one.
Problem two comes from our big brains, especially the big thinking part (the frontal lobe). We need HUGE heads to accommodate all them brains. You can see how big our heads are compared to our bodies, specially our hips!
So, small hips+big heads=trouble birthing. To get around this, we evolved to give birth basically as soon as our babies are ready to survive the atmosphere (can breathe and swallow by themselves), while still being small enough to pass through their mothers. That means we come out of the womb woefully undercooked, and need to grow up outside the womb to adulthood. Growing up outside the nice, cozy, nutrient rich environment of the placenta also takes some extra time, especially for these big brains we keep talking about to develop.
There have been studies suggesting our overall hip/head ratio has shrunken a bit since cesarean births have become widely available, because our hips would no longer become limiting factors to the size of our babies.
Latest Answers