A semi-educated observation from a sleep-deprived mother...

Most mothers can remember a time when their babies didn't understand the societal rules of Night and Day. For some strange reason, mothers are asked to not just loose sleep during their pregnancy, but after the birth of their babies, and then again when their children become teens. This means that if you were to have 4 kids spaced 3 years apart, than you would miss out on a good night sleep for about 30 years. 30 years ladies! Now add that to your own age and no wonder sleep comes so easily after middle age. That's a lot of catching up to do!