Today the neurology fellow in my small group session connected some dots I found interesting. Why do you faint when your brain isn’t getting enough oxygen? Well, it’s not just that there isn’t enough oxygen (the Darwinian approach could plausibly have been to channel blood to more important areas of the brain in the same way that your body can channel blood towards more critical areas of the body). Fainting actually works with gravity. You need blood in your head, keeping blood up high takes a certain level of pressure. You need less pressure if your head is low. If you faint, your head is likely to be lower to the ground.
Your body is a machine, and fainting is very literally an emergency low battery mode to force you to the ground so it takes less power keep you alive.
Kind of beautiful.