Some recent research suggests that normal human sleep has always been in one continuous block in places near the equator.  Then segmented sleep developed after humans migrated to places like Europe where sunrise&#x2F;sunset times vary more.  According to this hypothesis, segmented sleep was only a temporary phenomenon, before electric light caused a return to continuous sleep.<p><a href="https:&#x2F;&#x2F;athensscienceobserver.wordpress.com&#x2F;2015&#x2F;11&#x2F;24&#x2F;the-science-of-sleep-unraveling-biology-and-culture&#x2F;" rel="nofollow">https:&#x2F;&#x2F;athensscienceobserver.wordpress.com&#x2F;2015&#x2F;11&#x2F;24&#x2F;the-s...</a><p><a href="http:&#x2F;&#x2F;well.blogs.nytimes.com&#x2F;2015&#x2F;10&#x2F;15&#x2F;112251&#x2F;" rel="nofollow">http:&#x2F;&#x2F;well.blogs.nytimes.com&#x2F;2015&#x2F;10&#x2F;15&#x2F;112251&#x2F;</a>