Editing Concealed ovulation (section)

== Human females ==

In humans, an adult woman's fertility peaks for a few days during each roughly monthly cycle. The frequency and length of fertility (the time when a woman can become pregnant) is highly variable between women, and can slightly change 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 woman to estimate her own level of fertility at a given time ([[fertility awareness]]). Whether other humans, potential reproductive partners in particular, 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 a relatively small number of studies.

Several small studies have found that fertile women appear more attractive to men than women during infertile portions of her menstrual cycle, or women using [[hormonal contraception]].<ref name="Roberts et al 2004">{{cite journal |author1=S. C. Roberts |author2=J. Havlicek |author3=J. Flegr |author4=M. Hruskova |author5=A. C. Little |author6=B. C. Jones |author7=D. I. Perrett |author8=M. Petrie | title =  Female facial attractiveness increases during the fertile phase of the menstrual cycle | journal = [[Proceedings of the Royal Society B]] | volume = 271 | pages = S270–S272 |date=August 2004 | doi = 10.1098/rsbl.2004.0174 | pmid=15503991 | pmc=1810066 | issue=Suppl 5}}</ref><ref name="Miller et al 2007">{{cite journal |author1=Geoffrey Miller |author2=Joshua M. Tybur |author3=Brent D. Jordan | title = Ovulatory cycle effects on tip earnings by lap dancers: economic evidence for human estrous? | journal = Evolution and Human Behavior | volume = 28 | issue = 6 | pages = 375–381 |date=June 2007 | url = http://www.unm.edu/~gfmiller/cycle_effects_on_tips.pdf | access-date = 2008-01-21 | doi = 10.1016/j.evolhumbehav.2007.06.002  |citeseerx=10.1.1.154.8176 }}</ref> It has also been suggested that a woman's voice may become more attractive to men during this time.<ref name="Pipitone and Gallup 2008">{{cite journal | last = Pipitone | first = R. |author2=G . Gallup Jr | title = Women's voice attractiveness varies across the menstrual cycle | journal = Evolution and Human Behavior | volume = 29 | issue = 4 | pages = 268–274 | date = 2008-05-18 | doi = 10.1016/j.evolhumbehav.2008.02.001}}</ref> Two small studies of [[monogamy|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.<ref name="Bullivant et al 2004">{{cite journal|author=Susan B. Bullivant |title=Women's sexual experience during the menstrual cycle: identification of the sexual phase by noninvasive measurement of luteinizing hormone |journal=Journal of Sex Research |date=February 2004 |volume=41 |issue=1 |pages=82–93 |url=https://dx.doi.org/10.1080/00224490409552216 |archive-url=https://archive.today/20070728011531/http://www.findarticles.com/p/articles/mi_m2372/is_1_41/ai_n6032944 |url-status=dead |archive-date=2007-07-28 |pmid=15216427 |doi=10.1080/00224490409552216 |author2=Sarah A. Sellergren |author3=Kathleen Stern |display-authors=3 |last4=Spencer |first4=Natasha A. |last5=Jacob |first5=Suma |last6=Mennella |first6=Julie A. |last7=McClintock |first7=Martha K. |s2cid=40401379 |url-access=subscription }}</ref> It may be that a woman's awareness of men's courtship signals<ref>{{cite journal | last1 = Ann Renninger | first1 = Lee | last2 = Wade | first2 = T. Joel | last3 = Grammer | first3 = Karl | year = 2004 | title = Getting that female glance: Patterns and consequences of male nonverbal behavior in courtship contexts | journal = Evolution and Human Behavior | volume = 25 | issue = 6| pages = 416–431 | doi=10.1016/j.evolhumbehav.2004.08.006}}</ref> increases during her highly fertile phase due to an enhanced olfactory awareness of chemicals specifically found in men's body odor.<ref>{{cite journal | last1 = Thornhill | first1 = Randy | last2 = Gangestad | first2 = Steven W. | year = 1999 | title = The Scent of Symmetry: A Human Sex Pheromone that Signals Fitness? | journal = Evolution and Human Behavior | volume = 20 | issue = 3| pages = 175–201 | doi=10.1016/s1090-5138(99)00005-7}}</ref><ref>{{cite journal | last1 = Brooksbank | first1 = B. W. L. | year = 1962 | title = Urinary excretion of androst-16-en-3 alpha-ol in human male axillary sweat | doi = 10.1007/bf01938327 | journal = Experientia | volume = 30 | issue = 8| pages = 864–865 | pmid = 4416149 | s2cid = 44558005 }}</ref>

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).<ref name="Brewis and Meyer 2005">{{Cite journal | last1 = Brewis | first1 = A. | last2 = Meyer | first2 = M. | doi = 10.1086/430016 | title = Demographic Evidence That Human Ovulation is Undetectable (at Least in Pair Bonds) | journal = Current Anthropology | volume = 46 | issue = 3 | pages = 465–471 | year = 2005 | s2cid = 30243603 }}</ref> This is contrary to other studies, which have found female sexual desire and [[extra-pair copulation]]s (EPCs) to increase during the midfollicular to ovulatory phases (that is, the highly fertile phase).<ref>{{cite journal | last1 = Regan | first1 = P. C. | year = 1996 | title = Rhythms of desire: the association between menstrual cycle phases and female sexual desire | journal = Canadian Journal of Human Sexuality | volume = 5 | pages = 145–156 }}</ref> 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 hormonal changes causing her to feel increased sexual desire), contrasting with the man's inability to detect ovulation because of its being "hidden".{{Citation needed|date=May 2022}}
  
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.<ref name="Mothluk 2006">{{cite journal | last = Motluk | first = Alison | title = The secret life of semen | journal = New Scientist | issue = 2563 | date = 2006-08-05 | url = http://www.eurekalert.org/pub_releases/2006-08/ns-tsl080206.php | access-date = 2008-06-28}}</ref> One group of authors has theorized that concealed ovulation and menstruation were key factors in the development of [[symbolic culture]] in early human society.<ref name="Knight 1991">{{cite book | author = Chris Knight | title = Blood relations: menstruation and the origins of culture | publisher = Yale University Press | location = New Haven, Conn | year = 1991 | isbn = 978-0-300-04911-4}}</ref><ref name="Knight 1995">{{cite journal | last = Knight | first = Chris | author2 = Camilla Power | author3 = Ian Watts | title = The Human Symbolic Revolution: A Darwinian Account | journal = Cambridge Archaeological Journal | volume = 5 | issue = 1 | pages = 75–114 | year = 1995 | url = http://www.radicalanthropologygroup.org/pub_knight_power_watts_big.pdf | access-date = 2006-12-13 | doi = 10.1017/S0959774300001190 | s2cid = 54701302 | archive-date = 2020-08-01 | archive-url = https://web.archive.org/web/20200801052656/http://radicalanthropologygroup.org/sites/default/files/pdf/pub_knight_power_watts_big.pdf | url-status = dead }}</ref>