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Article: Diurnal
- Article from:
- Animal Sciences
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CopyrightCOPYRIGHT 2002 The Gale Group Inc. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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Diurnal
Diurnal organisms are those that are active mainly during the day. When activity patterns of an organism occur in cycles of about twenty-four hours, the pattern is called a circadian rhythm. Diurnal animals, which sleep during the night and are active during the day, or, conversely, nocturnal animals, which sleep during the day and are active at night, follow a circadian rhythm. Scientists believe that circadian rhythms are controlled by an internal timing mechanism called a biological clock. The exact nature of this internal timing is not known, but varying levels of hormones are thought to play a role.
Scientists generally concur that the evolution of species on Earth has ...