Why do some people need more sleep than others?

Why do some people need more sleep than others?

We have no idea why these individual differences really arise. Why one can have short sleepers or long sleepers. One question you asked earlier was how much sleep do we need? If one takes the population average, we'd say that most people sleep about seven and a half hours during the night, then plus/minus 2 hours. So a range of five and a half to nine and a half hours will still encompass a huge chuck of the population. It isn't until you move further out that you're down to the three, three and a half hour REM set. That's really quite unusual. But why the differences emerge we're not sure.