 So that's sort of the more recent picture of it. I don't know if you want to get way further back, because I start where life started on Earth 3.5 billion years ago, but that's a synopsis of how one-way evolution can work. So I read once where the birth canal had a lot to do with the part of our brain that evolved, because the larger the head, the easier the heart of the birth, so we had to accommodate by having our physiology change.