263:, regardless of whether an egg becomes fertilized or successfully implants in the uterus. This produces more unneeded material per cycle than in non-menstruating mammals, which may explain why the extra material is not simply reabsorbed as done by those species. In essence, menstruating animals treat every cycle as a possible pregnancy by thickening the protective layer around the endometrial wall, while non-menstruating placental mammals do not begin the pregnancy process until a fertilized egg has implanted in the uterine wall.
276:.This triggers epigenetic changes that prevent formation of the placenta, which prevents the embryo from implanting and leaves it to be removed in the next menstruation. This failsafe mode is not possible in species where decidualization is controlled by hormonal triggers from the embryo. This is sometimes referred to as the choosy uterus theory, and it is theorized that this positive outweighs the negative impacts of menstruation in species with high aneuploidy rates and hence a high number of 'doomed' embryos.
280:
317:(AI) is used for breeding, the AI technician's time can be used more efficiently, by breeding several females at the same time. In order to induce estrus, a variety of techniques have been tried in recent years, involving both more natural, and more hormonal based methods. Different ways of injecting or feeding hormones to livestock are costly, and have variable success rates.
255:, and is usually triggered by hormones released by the embryo. In humans, decidualization happens spontaneously at the beginning of each menstrual cycle, triggered by hormonal signals from the ovaries. For this reason, the human uterine lining becomes fully thickened during each cycle as a defense to
1459:
Teklenburg, Gijs; Salker, Madhuri; Molokhia, Mariam; Lavery, Stuart; Trew, Geoffrey; Aojanepong, Tepchongchit; Mardon, Helen J.; Lokugamage, Amali U.; Rai, Raj; Landles, Christian; Roelen, Bernard A. J.; Quenby, Siobhan; Kuijk, Ewart W.; Kavelaars, Annemieke; Heijnen, Cobi J. (2010-04-21). Vitzthum,
271:
events result in stillbirth or miscarriage, there is an evolutionary advantage to ending the pregnancy early, rather than nurturing a fetus that will later miscarry. There is evidence to show that some abnormalities in the developing embryo can be detected by endometrial stromal cells in the uterus,
242:
There are varying views on evolution of overt menstruation in humans and related species, and the evolutionary advantages in losing blood associated with dismantling the uterine lining rather than absorbing it, as most mammals do. The reason is likely related to differences in the ovulation process.
312:
For breeding livestock, there are a number of advantages to be gained by finding methods to induce ovulation on a planned schedule, and thus synchronize the estrus cycle between many female animals. If animals can be bred on the same schedule, it increases convenience for the livestock owner, since
266:
For this reason, it is speculated that menstruation is a side effect of spontaneous decidualization, which evolved in some placental mammals due to its advantages over non-spontaneous decidualization. Spontaneous decidualization allows for more maternal control in the maternal-fetal conflict by
250:
have a uterine lining that builds up when the animal begins ovulation, and later further increases in thickness and blood flow after a fertilized egg has successfully implanted. This final process of thickening is known as
308:
The female will ovulate spontaneously and be receptive to the male to be bred (express estrus) at regular biologically defined intervals. The female is receptive to males only while experiencing estrus.
113:. Many zoologists regard this as different from a "true" menstrual cycle. Female domestic animals used for breeding—for example dogs, pigs, cattle, or horses—are monitored for physical signs of an
686:
267:
increasing selectivity over the implanted embryo. This may be necessary in humans and other primates, due to the abnormally large number of genetic disorders in these species. Since most
1592:
Zhang X, Zhu C, Lin H, Yang Q, Ou Q, Li Y, Chen Z, Racey P, Zhang S, Wang H (August 2007). "Wild fulvous fruit bats (Rousettus leschenaulti) exhibit human-like menstrual cycle".
171:. Overt menstruation (where there is blood flow from the vagina) occurs primarily in humans and close evolutionary relatives such as chimpanzees. Some species, such as domestic
525:
Gras, Lyn, et al. "The incidence of chromosomal aneuploidy in stimulated and unstimulated (natural) uninseminated human oocytes." Human
Reproduction 7.10 (1992): 1396-1401.
239:
have a menstrual cycle. As these groups are not closely related, it is likely that four distinct evolutionary events have caused menstruation to arise.
1263:
Bellofiore N, Ellery SJ, Mamrot J, Walker DW, Temple-Smith P, Dickinson H (January 2017). "First evidence of a menstruating rodent: the spiny mouse (
1241:
693:
1661:) G. L. HUNTER, P. C. BELONJE and C. H. VAN NIEKERK, Department of Agricultural Technical Services, Stellenbosch, Agroanimalia 3,133-140 (1971)
1319:"The evolution of menstruation: a new model for genetic assimilation: explaining molecular origins of maternal responses to fetal invasiveness"
960:
1094:"Women's sexual experience during the menstrual cycle: identification of the sexual phase by noninvasive measurement of luteinizing hormone"
211:(reproductive-age females are in heat for 75% of their menstrual cycle) has a similar effect to the lack of a "heat" in human females.
1755:
1646:
Synchronized mating and lambing in spring-bred Merino sheep: the use of progestogen-impregnated intravaginal sponges and teaser rams
1462:"Natural Selection of Human Embryos: Decidualizing Endometrial Stromal Cells Serve as Sensors of Embryo Quality upon Implantation"
1142:
283:
Phylogeny tree of menstruating and select non-menstruating mammals. Each color indicates a convergent evolutionary event: green,
1183:
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874:
40:
Although there is some disagreement in definitions between sources, menstruation is generally considered to be limited to
1527:
163:, if no fertilization takes place, the uterus reabsorbs the endometrium. This breakdown of the endometrium without
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also lack visible signs of impending ovulation. Also, it has been said that the extended estrus period of the
109:, in which the endometrium is completely reabsorbed by the animal (covert menstruation) at the end of its
1233:
536:
201:), whether men can detect fertility in women is debated; recent studies have given conflicting results.
1740:
1092:
Bullivant SB, Sellergren SA, Stern K, Spencer NA, Jacob S, Mennella JA, McClintock MK (February 2004).
989:
Roberts SC, Havlicek J, Flegr J, Hruskova M, Little AC, Jones BC, Perrett DI, Petrie M (August 2004).
1606:
765:"Characteristics of the endometrium in menstruating species: lessons learned from the animal kingdom"
1053:
1750:
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314:
1601:
1048:
964:
892:
Profet M (September 1993). "Menstruation as a defense against pathogens transported by sperm".
576:
Profet M (September 1993). "Menstruation as a defense against pathogens transported by sperm".
1645:
1206:
Stanford CB (March–April 2000). "The Brutal Ape vs. the Sexy Ape? The Make-Love-Not-War Ape".
1085:
1034:"Ovulatory cycle effects on tip earnings by lap dancers: economic evidence for human estrus?"
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while approaching heat; this discharge has a different physiologic cause than menstruation.
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Females of most mammal species advertise fertility to males with visual behavioral cues,
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991:"Female facial attractiveness increases during the fertile phase of the menstrual cycle"
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1417:"Cyclic Decidualization of the Human Endometrium in Reproductive Health and Failure"
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Strassmann BI (June 1996). "The evolution of endometrial cycles and menstruation".
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Bellofiore N, Cousins F, Temple-Smith P, Dickinson H, and Evans J (July 2018).
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197:). In humans, while women can learn to recognize their own level of fertility (
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147:. In species that experience estrus, females are generally only receptive to
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33:). It occurs on a regular basis in uninseminated sexually reproductive-age
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Bellofiore N, Cousins F, Temple-Smith P, Dickinson H, Evans J (July 2018).
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1553:"A missing piece: the spiny mouse and the puzzle of menstruating species"
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537:"A missing piece: the spiny mouse and the puzzle of menstruating species"
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692:. European Society of Human Reproduction and Embryology. Archived from
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the young animals will be at the same stage of development. Also, if
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A few mammals do not experience obvious, visible signs of fertility (
1368:"The evolution of human reproduction: A primatological perspective"
905:
733:
621:"The evolution of human reproduction: a primatological perspective"
589:
247:
160:
1528:"The 'choosy uterus': New insight into why embryos do not implant"
985:
Studies that found women are more attractive to men when fertile:
963:. Mar Vista Animal Medical Center. 2 February 2008. Archived from
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41:
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208:
91:
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45:
34:
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139:, or both. This period of advertised fertility is known as
94:) is found primarily in humans and close relatives such as
1178:. Berkeley: University of California Press. p. 107.
288:
172:
69:
57:
86:. Overt menstruation (where there is bleeding from the
939:. Redmon, OR: Current Conceptions, Inc. p. 146.
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Average length (days) of estrus and estrous cycles:
117:
period, which indicates that the animal is ready for
1316:
1031:
867:Why is sex fun?: the evolution of human sexuality
1727:
1414:
961:"Canine False Pregnancy and Female Reproduction"
1650:
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1269:American Journal of Obstetrics and Gynecology
667:
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1317:Emera D, Romero R, Wagner G (January 2012).
814:
812:
810:
715:
713:
1415:Gellersen B, Brosens JJ (1 December 2014).
1143:"Orangutans: Reproduction and Life History"
1032:Miller G, Tybur JM, Jordan BD (June 2007).
1669:
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124:
1719:"Managing the Sow and Gilt Estrous Cycle"
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64:primates and possibly weakly present in
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68:. Beyond primates, it is known only in
29:is the shedding of the uterine lining (
16:Periodic shedding of the uterine lining
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182:
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1088:is not affected by female fertility:
937:Pathways to Pregnancy and Parturition
227:, yet only ten primate species, four
1716:
1244:from the original on 27 January 2013
1149:. Harvard University. Archived from
272:but only upon differentiation into
13:
1557:Journal of Molecular Endocrinology
1449:
1063:10.1016/j.evolhumbehav.2007.06.002
763:Catalini L, Fedder J (June 2020).
541:Journal of Molecular Endocrinology
14:
1767:
1756:Mammal female reproductive system
1692:
995:Proceedings. Biological Sciences
19:For menstruation in humans, see
1701:"Estrous Cycle Learning Module"
1699:Rasby, Rick; Vinton, Rosemary.
1638:
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1408:
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1226:
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1147:Gunung Palung Orangutan Project
1078:
979:
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928:
894:The Quarterly Review of Biology
837:
722:The Quarterly Review of Biology
578:The Quarterly Review of Biology
1366:Martin RD (28 November 2007).
1172:Lanting F, de Waal FB (1997).
756:
678:
668:Coutinho EM, Segal SJ (1999).
661:
612:
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519:
175:, experience small amounts of
1:
1616:10.1095/biolreprod.106.058958
844:Mikkelson DP (29 June 2007).
513:
60:), but completely lacking in
1487:10.1371/journal.pone.0010258
1041:Evolution and Human Behavior
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101:Females of other species of
7:
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235:, and one known species of
37:of certain mammal species.
10:
1772:
1710:"The Mare's Estrous Cycle"
1652:Met opsomming in Afrikaans
1281:10.1016/j.ajog.2016.07.041
1234:"Why do women menstruate?"
674:. Oxford University Press.
186:
155:are an exception). In the
128:
18:
1175:Bonobo: the forgotten ape
1110:10.1080/00224490409552216
869:. London: HarperCollins.
671:Is menstruation obsolete?
1717:May, Jerry; Bates, Ron.
151:while they are in heat (
1677:. University of Wyoming
1658:Avec resume en francais
1594:Biology of Reproduction
1098:Journal of Sex Research
769:Biology of Reproduction
687:"Course 4:Implantation"
315:artificial insemination
125:Estrus and menstruation
1657:
1651:
1335:10.1002/bies.201100099
1084:Study that found male
1007:10.1098/rsbl.2004.0174
782:10.1093/biolre/ioaa029
300:
304:Animal estrous cycles
282:
1434:10.1210/er.2014-1045
861:, which references:
685:Bischof P, Cohen M.
167:is sometimes called
1570:10.1530/jme-17-0278
1478:2010PLoSO...510258T
1460:Virginia J. (ed.).
1275:(1): 40.e1–40.e11.
1001:(Suppl 5): S270–2.
865:Diamond JM (1997).
554:10.1530/JME-17-0278
259:penetration of the
199:fertility awareness
195:concealed ovulation
189:concealed ovulation
183:Concealed ovulation
169:covert menstruation
1708:Mottershead, Jos.
1385:10.1002/ajpa.20734
1220:10.1511/2000.2.110
1208:American Scientist
967:on 15 October 2008
935:Senger PL (2012).
638:10.1002/ajpa.20734
619:Martin RD (2007).
301:
111:reproductive cycle
44:. It is common in
1741:Animal physiology
1532:medicalxpress.com
1421:Endocrine Reviews
1185:978-0-520-20535-2
1153:on April 21, 2008
946:978-0-9657648-3-4
876:978-0-465-03127-6
846:"Buried Pleasure"
824:Britannica Online
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