No other mammal does this, and only some human cultures do it. When did it start? Parents put their baby in a crib in a separate room, and it wails in terror because it needs it's mothers body, and it doesn't have a concept of time. It can't know that someone will come back later. It usually takes several months for the baby's spirit to be completely murdered to the point where they no longer cry. They've given up hope. But why did parents start having their babies sleep in separate rooms? How did that start? I've looked it up everywhere, and i've found no solid info.