From time to time we read about people who sleep three or four hours per day day. E.g. Thatcher, Churchill, Arafat, Edison etc. all slept just a few hours per day (about four hours if I remember correctly). Another example: So, it looks like most people who need 7 to 8 hours sleep are not sleeping efficiently. But then the question is why evoluton did not lead to more efficient sleep for most people? Is it because less efficient sleep leads to people spending more time in bed leading to more sex and thus more children?