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Chronobiology is a field of biology that examines time-related phenomena in living organisms. These cycles are important in many essential biological processes that occur in a "scheduled" fashion, such as eating, sleeping, mating, hibernating, migration, and cellular regeneration.

The most important rhythm in chronobiology is the circadian rhythm, which refers to the 24-hour daily biological cycle; however, many other important cycles are also studied, including:

  • Infradian rhythms[?], which are long-term cycles, such as the annual migration or reproduction cycles found in certain animals or the monthly menstrual cycle of human females.
  • Ultradian rhythms[?], which are short cycles, such as the 90-minute REM cycle in sleep or the 3 hour cycle of growth hormone production.
  • Tidal rhythms[?], commonly observed in marine life, which follow the (roughly) 12-hour transition from high to low tide and back.

Related to, but not part of, chronobiology is the unsubstantiated theory of biorhythms, which are said to be a set of cyclic variations in human behaviour. The theory has no known physiological basis, and is considered by most people to be pseudoscience.


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Thomas a Kempis

... should be invoked. He also gives prayers to Mary (cf. the De tabernaculis, and Hortus rosarum, Pohl's ed., ut inf., i. also iii. 357, vi. 219, 235 sqq.). External ...

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