title: Common 30-day multiple in gestation time of terrestrial placentals.
abstract: 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.
authors.affiliation: Department of Psychology, Pennsylvania State University, University Park 16802.
authors.forename: F M
authors.initials: FM
authors.lastname: Brown
mesh_terms: D000818:Animals; D055580:Astronomical Phenomena; D001256:Astronomy; D005260:Female; D006801:Humans; D010507:Periodicity; D010920:Placenta / Q000502:physiology*; D011247:Pregnancy / Q000502:physiology*; D011270:Pregnancy, Animal / Q000502:physiology*; D012098:Reproduction; D013045:Species Specificity