Editing Sleep (section)

=== Social timing ===
Humans are also influenced by aspects of ''social time'', such as the hours when other people are awake, the hours when work is required, the time on clocks, etc. [[Time zone]]s, standard times used to unify the timing for people in the same area, correspond only approximately to the natural rising and setting of the sun. An extreme example of the approximate nature of time zones is China, a country which used to span five time zones and now [[Time in China|officially uses only one]] (UTC+8).<ref name=RonnenbergEtAl2007 />