WE USED TO SLEEP TWICE EACH NIGHT – 6/30/15

While it's dated "6/30/15", it's an "encore selection -- from Dreamland: Adventures in the Strange Science of Sleep", published in 2012.

The topic has hit the pages of HN before. From a bit over two years ago are the 107 comments at https://news.ycombinator.com/item?id=5542453 . One of the commenters there pointed to the 2009 paper "In short photoperiods, human sleep is biphasic", at http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2869.1992.... . More background on Wehr's argument for biphasic sleep is at https://en.wikipedia.org/wiki/Segmented_sleep and http://www.bbc.com/news/magazine-16964783 .