Why sleep?

Many ask, but few answer. We present two of science's most intriguing theories.

Richard Gallagher
Mar 31, 2009

Sleep takes up around a third of our lives, and is an object of fascination during the other two thirds. "I dreamt that..." is surely among the top 10 conversation topics of all time.

Given this, it is surprising how little attention is paid to the anthropology of sleep. Intriguing (but too little) work has been done on sleep practices in nonindustrialized societies,1 and there has been some engaging speculation about sleep patterns;2 it all points to our Western conventions as being a behavioral outlier.

We condense our sleep into a single lengthy stint, in which any interruption is considered to be a pathology, while our forebears and preindustrialized societies enjoy segmented sleep. They also display a fuzzy "continuum of arousal...from...disengaged semialert, to somnolence or drowsing, to dozing, to napping,"1 while we tend to...


1. C.M. Worthman and M. Melby, "Toward a comparative developmental ecology of human sleep." In: M.A. Carskadon, ed. Adolescent Sleep Patterns: Biological, Social, and Psychological Influences. New York: Cambridge University Press, pp. 69–117. 2. A. Roger Ekirch, At Day's Close: Night in Times Past. New York: W. W. Norton, 2006. 3. David M. Raizen et al., "Lethargus is a Caenorhabditis elegans sleep-like state," Nature 2008;451:569–72.