This is interesting because monophasic sleep cycles are not really natural.
When human babies are born they adopt a polyphasic cycle. By the time that they are about one year old they have adopted a biphasic cycle. Many cultures have adopted a biphasic cycle (think about the siesta in Sothern Europe). It is interesting that adult great apes also adopt a biphasic cycle.
Northern Europeans have generally adopted the monophasic cycle and this could be an adaption to the short day length in winter.
Many experiments have been done using polyphasic cycles. Different results have been obtained by different groups but this is probably down to different tests and testing techniques. It does appear that over a long period a polyphasic cycle limits the amount of working memory available in the brain and also results in microsleep during waking periods. This is not a good idea if the person microsleeping is performing dangerous tasks such as driving.
