They don't have the muscles or nerves or the connection between them? All three? Animals can walk within days, most of them. I read somewhere that some part of the motor system doesn't mature till the person is in their 20s! That can't be true, but unfortunately I can't find any information on this question. I've done all sorts of google searches, for things like "newborn" "motor neurons" "motor cortex" "muscles" "walking" etc. I had not success. Appreciate any help.