Common 30-day multiple in gestation time of terrestrial placentals

Frederick M. Brown

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


Weekly, twice-monthly, and monthly lunar related rhythms have been alleged for various animal reproductive processes. Herein gestation times of 213 types of terrestrial placental mammals were analyzed for best-fit integer multiples approximating length of any of the above lunar related rhythms. At the same time numeric controls were constituted of a completely random, a block randomized, and a sequential set of numbers spanning the data set. Among test integers 6 through 33, the number 30, approximating the 29.53-day lunar-synodic month, was consistently and statistically a best-fit multiple to the data. This might suggest a once-monthly lunar illumination, but not a twice-monthly gravitational or near-weekly tidal, influence upon animal reproduction. As for a receptor mechanism, the tapetum, or reflective layer of the retina, present in most land mammals, but absent in humans, enhances dim illumination. A suggestion is that because of this visual enhancer, cycling moonlight might be a circa-lunar physiologic timer for many terrestrial mammals.

Original languageEnglish (US)
Pages (from-to)195-210
Number of pages16
JournalChronobiology International
Issue number3
StatePublished - Jan 1 1988

All Science Journal Classification (ASJC) codes

  • Physiology
  • Physiology (medical)


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