Just for clarification, when I say bi-phasic, I mean sleeping possibly not much after when the sun goes down, waking up for an hour or so (reading, eating, whatever), and then waking up almost around the crack of dawn.
I relate it to being healthier in many ways. One thing that I think is a must for this to work is getting lots of sunlight during the day. This seems to trigger correct patterns in your body. JUST personal experience and opinion though.
I realize this doesn't work everywhere. In Alaska for example, I would be screwed. I think you might hypothesize that sleeping patterns can be somewhat dictated by where you live on Earth? (in other words, length of daylight and temperature)