Physiologically, why do some people function fine on 5 hours of sleep per night while others need 8 or 10 hours?

Luke Newman 

Researchers in California examined a woman and daughter who routinely slept between five and six hours per night.  To examine why they needed less sleep, the researchers determined that it would be most effective to compare the mother and daughter with the rest of the family, who utilized more “normal” sleep schedules.  They performed blood and DNA analyses for all members of the family.  The DNA tests showed that the mother and daughter shared a mutation in their genetic code that the other members of the family did not have (point mutation in gene hDEC2, a gene which is associated with sleep patterns).  This could merely be a coincidence, so the scientists created the same gene mutation in laboratory mice.  Their findings showed that the mutated mice slept less than mice that did not receive the same gene mutation.  This may not be the definitive answer to the question, as there are probably more factors involved than just one gene mutation, but it does show one possible contribution to this physiological situation.

Source: http://www.independent.co.uk/news/science/so-why-do-some-people-need-such-little-sleep-1771873.html