Segmented Sleep Used To Be The Norm
Historian A. Roger Ekirch brought the trend of segmented sleep to light in 2001. His findings revealed that people used to divide their sleep into two separate periods, often referred to as "first sleep" and "second sleep." Between these periods, people would do chores, read, pray, or even go outside to visit friends. As electric lighting became more prominent, however, people began to stay up later and get their sleep all in one go.
from The Good Stuff
Key Facts In This Video
There is no solid scientific consensus on why we sleep. (1:56)
Black rhinos sleep for one to two hours laying down, and three to four hours standing up. (4:23)
Dolphins engage in unihemispheric sleep, which means that one half of the brain is resting while the other half is alert. (8:01)