Abstract
Seven-day cycles in spontaneous activity were found in recently trapped Norway rats, chipmunks, ground squirrels, and squirrel monkeys [Rattus norvegicus, Tamais striatus, Citellus tridecemlineatus, Saimiri sciureus], but not in tame domesticated laboratory Norway rats and hamsters [Mesocricetus auratus]. This 7 day cycle was a function of emotional reactions of the wild animals to hitherto overlooked slight differences in activities of relevant human beings between weekdays and weekends. Elimination of the ability of wild animals to react to slight environment differences by blinding or deafening abolished the 7 day cycles. No definite evidence has been found for the presence of inherent 7 day cycles in animals or man.

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