Artifactual seven-day cycles in spontaneous activity in wild rodents and squirrel monkeys.

Seven-day cycles in spontaneous activity were found in wild animals (recently trapped Norway rats, chipmunks, ground squirrels, and squirrel monkeys), but not in tame domesticated animals (laboratory Norway rats and hamsters). This 7-day cycle turned out to be a function of emotional reaction of the wild animals to hitherto overlooked slight differences in activities of relevant human beings between weekdays and weekends. Elimination of 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.