Evolutionary theories often emphasize that the humans have adapted to their physical environment. One such theory hypothesizes that people must spontaneously follow 24 hours cycle of sleeping and walking-even if they're not exposed to usual pattern of sunlight. To test this notion, eight paid volunteers were placed (individually) in room in which there was no light from outside and no clocks or other indication of time. They could turn the lights on and off as they wished. After the month in the room each individual tended to make a steady cycle. Their cycles at the end of the study were as follows: 25, 27, 25, 23, 24, 26, and 25.

Using 5% level of significance, what must we conclude about theory that 24 hours is natural cycle? (That is, does the average cycle length under these conditions differ significantly from 24 hours?).

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