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Concealed ovulation or hidden estrus in a species is the lack of any perceptible change in an adult female (for instance, a change in appearance or scent) when she is "in heat" and near ovulation. Some examples of such changes are swelling and redness of the genitalia in baboons and bonobos ''Pan paniscus'', and pheromone release in the feline family. In contrast, the females of humans and a few other species have few external signs of fecundity, making it difficult for a mate to consciously deduce, by means of external signs only, whether or not a female is near ovulation. In humans, adult women's fertility peaks for a few days during each monthly cycle. Human females actually experience a wide range of menstrual cycle lengths and frequencies, so the notion of a monthly cycle is better considered an average or shorthand; therefore, the frequency and length of fertility (the time when a woman can become pregnant) is highly variable between women and for each woman over the course of her lifespan. Humans are considered to have "concealed ovulation" because there is no outward physiological sign, either to a woman herself or to others, that ovulation, or biological fertility, is occurring. Knowledge of the fertility cycle, learned through experience or from educational sources, can allow a women to estimate her own level of fertility at a given time (fertility awareness). Whether other humans, in particular, potential reproductive partners (assumed to be men), can detect fertility in women through behavioral or invisible biological cues is highly debated. Scientists and laypersons are interested in this question because it has implications for human social behavior, and could theoretically offer biological explanations for some human sexual behavior. However, the science here is weak, due to 1) a relatively small number of studies, and 2) biases in the studies due to the researchers's reliance on male-centered concepts of reproduction and attractiveness, heterosexual sexuality, and Euroamerican cultural norms of kinship and courtship. Several small studies have found that fertile women (compared to women in infertile portions of the menstrual cycle, or using hormonal contraception) appear more attractive to men. It has also been suggested that a woman's voice may become more attractive to men during this time. Two small studies of monogamous human couples found that women initiated sex significantly more frequently when fertile, but male-initiated sex occurred at a constant rate, without regard to the woman's phase of menstrual cycle. It may be that a woman's awareness of men's courtship signals〔Lee Ann Renninger, T. Joel Wade, Karl Grammer "Getting that female glance: Patterns and consequences of male nonverbal behavior in courtship contexts" Evolution and Human Behavior 25 (2004) 416–431〕 increases during her highly fertile phase due to an enhanced olfactory awareness of chemicals specifically found in men's body odor.〔Randy Thornhill and Steven W. Gangestad "The Scent of Symmetry: A Human Sex Pheromone that Signals Fitness?" Evolution and Human Behavior 20: 175–201 (1999)〕〔Brooksbank, B.W.L. Urinary excretion of androst-16-en-3 alpha-ol in human male axillary sweat. Experientia 30:864–865, 1962.〕 Analyses of data provided by the post-1998 U.S. Demographic and Health Surveys found no variation in the occurrence of coitus in the menstrual phases (except during menstruation itself). This is contrary to other studies, which have found female sexual desire and extra-pair copulations ("EPC's") to increase during the midfollicular to ovulatory phases (that is, the highly fertile phase).〔Regan, P.C. Rhythms of desire: the association between menstrual cycle phases and female sexual desire. Canadian Journal of Human Sexuality 5:145–156, 1996.〕 These findings of differences in woman-initiated versus man-initiated sex are likely caused by the woman’s subconscious awareness of her ovulation cycle (because of hormone changes causing her to feel increased sexual desire), contrasting with the man’s inability to detect ovulation because of its being “hidden”. In 2008, researchers announced the discovery in human semen of hormones usually found in ovulating women. They theorized that follicle stimulating hormone, luteinising hormone, and estradiol may encourage ovulation in women exposed to semen. These hormones are not found in the semen of chimpanzees, suggesting this phenomenon may be a human male counter-strategy to concealed ovulation in human females. Other researchers are skeptical that the low levels of hormones found in semen could have any effect on ovulation. One group of authors has theorized that concealed ovulation and menstruation were key factors in the development of symbolic culture in early human society. == Evolutionary hypotheses == Most primates have semiconcealed ovulation, which could be taken as evidence that the common ancestor had semiconcealed ovulation (still found today in gorillas), and that subsequently fully concealed ovulation evolved in humans, while fully "advertised" ovulation evolved in chimpanzees (see Homininae and "Why is Sex Fun?"). Evolutionary psychologists have advanced a number of different possible explanations for concealed ovulation (and elements of several hypotheses may be true). Some posit that the lack of signaling in some species is a trait retained from evolutionary ancestors, not something that existed previously and later disappeared. If signaling is supposed to have existed and was lost, then it could have been merely due to reduced adaptive importance and lessened selection, or due to direct adaptive advantages for the concealment of ovulation. Yet another possibility (regarding humans specifically) is that while highly specific signaling of ovulation is absent, human female anatomy evolved to mimic permanent signaling of fertility. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Concealed ovulation」の詳細全文を読む スポンサード リンク
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