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Anderson KA, Teichroeb JA, Ramsay MS, Bădescu I, López-Torres S, Gibb JK. Same-sex sexual behaviour among mammals is widely observed, yet seldomly reported: Evidence from an online expert survey. PLoS One 2024; 19:e0304885. [PMID: 38900815 PMCID: PMC11189198 DOI: 10.1371/journal.pone.0304885] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Accepted: 05/20/2024] [Indexed: 06/22/2024] Open
Abstract
Same-sex sexual behaviour (SSSB) occurs in most animal clades, but published reports are largely concentrated in a few taxa. Thus, there remains a paucity of published reports for most mammalian species. We conducted a cross-sectional expert survey to better understand the underlying reasons for the lack of publications on this topic. Most respondents researched Primates (83.6%, N = 61), while the rest studied Carnivora (6.9%, N = 5), Rodentia (4.1%, N = 3), Artiodactyla (2.7%, N = 2), and Proboscidea (2.7%, N = 2). Most respondents (76.7%, N = 56) had observed SSSB in their study species, but only 48.2% (N = 27) collected data on SSSB, and few (18.5%, N = 5) had published papers on SSSB. Of the unique species identified as engaging in SSSB in the survey, 38.6% (N = 17) have no existing reports of SSSB to the knowledge of the authors. In both the survey questions and freeform responses, most respondents indicated that their lack of data collection or publication on SSSB was because the behaviours were rare, or because it was not a research priority of their lab. No respondents reported discomfort or sociopolitical concerns at their university or field site as a reason for why they did not collect data or publish on SSSB. Multiple logistic regressions were performed to assess whether taxa studied, education level, or identification within the LGBTQ+ community predicted observing, collecting data on, or publishing on SSSB, but none of these variables were significant predictors. These results provide preliminary evidence that SSSB occurs more frequently than what is available in the published record and suggest that this may be due to a publishing bias against anecdotal evidence.
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Affiliation(s)
- Karyn A. Anderson
- Department of Anthropology, University of Toronto, Toronto, Ontario, Canada
| | - Julie A. Teichroeb
- Department of Anthropology, University of Toronto, Toronto, Ontario, Canada
| | - Malcolm S. Ramsay
- Department of Anthropology, University of Toronto, Toronto, Ontario, Canada
| | - Iulia Bădescu
- Département D’anthropologie, Université de Montréal, Montréal, Québec, Canada
| | - Sergi López-Torres
- University of Warsaw, Faculty of Biology, Biological and Chemical Research Centre, Institute of Evolutionary Biology, Warsaw, Poland
- Division of Paleontology, American Museum of Natural History, New York, NY, United States of America
| | - James K. Gibb
- Department of Anthropology, Northwestern University, Evanston, Illinois, United States of America
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Cunningham E, Benítez ME. From pathology to pleasure: Reframing mechanistic studies on same-sex sexual behavior in primates. Horm Behav 2024; 160:105476. [PMID: 38278061 DOI: 10.1016/j.yhbeh.2024.105476] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 12/11/2023] [Accepted: 01/07/2024] [Indexed: 01/28/2024]
Abstract
Same-sex sexual behaviors (SSB) in primates have historically been studied as sexual perversions, evolutionary paradoxes, and hormone-driven pathologies. Researchers in recent decades have challenged these perspectives, yet some of the original biases still linger. In this paper, we examine how the study of endocrinological mechanisms in SSB has been influenced by the historical framework of pathology. Societal attitudes and cultural conceptions of human sexuality have led researchers to study SSB in primates as the outcome of "abnormal" processes of "feminization" or "masculinization" of sexual behavior. Here, we argue for a renewed attention to other areas of inquiry regarding the relationship between hormones and SSB, such as the role of pleasure. We briefly review how current knowledge on the neuroendocrinology of pleasure in nonhuman primates may relate to the expression of SSB and highlight oxytocin and dopamine as potentially fruitful areas for future research. We argue that future studies on SSB in primates would benefit from 1) acknowledging how the historical study of SSB as a pathology has shaped mechanistic studies and 2) studying SSB with the same holistic approach as is taken with different-sex sexual behavior (DSB).
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Affiliation(s)
- Evan Cunningham
- Department of Anthropology, Emory University, Atlanta, GA, United States of America
| | - Marcela E Benítez
- Department of Anthropology, Emory University, Atlanta, GA, United States of America.
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Pfau D, Jordan CL, Breedlove SM. The De-Scent of Sexuality: Did Loss of a Pheromone Signaling Protein Permit the Evolution of Same-Sex Sexual Behavior in Primates? ARCHIVES OF SEXUAL BEHAVIOR 2021; 50:2267-2276. [PMID: 31016493 DOI: 10.1007/s10508-018-1377-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2018] [Revised: 12/12/2018] [Accepted: 12/13/2018] [Indexed: 05/15/2023]
Abstract
Primate same-sex sexual behavior (SSSB) is rarely observed in strepsirrhine species, and only somewhat more common in platyrrhines, but is observed in nearly all catarrhine species, including humans, suggesting the common catarrhine ancestor as the origin of routine SSSB. In mice, disruption of the transient receptor potential cation channel 2 (TRPC2) gene, which is crucial for transducing chemosensory signals from pheromones in the vomeronasal organ, greatly increased the likelihood of SSSB. We note that catarrhine primates share a common deleterious mutation in this gene, indicating that the protein was dysfunctional in the common catarrhine ancestral primate approximately 25 mya (million years ago). We hypothesize that the loss of this protein for processing pheromonal signals in males and females made SSSB more likely in a primate ancestral species by effectively lifting a pheromonally mediated barrier to SSSB and that this was an important precursor to the evolution of such behavior in humans. Additional comparisons between SSSB and the functional status of the TRPC2 gene or related proteins across primate species could lend support to or falsify this hypothesis. Our current research indicates that loss of TRPC2 function in developing mice leads to the loss or attenuation of sexually dimorphisms in the adult brain, which may help us to understand the biological underpinnings of SSSB. Our hypothesis offers an ultimate evolutionary explanation for SSSB in humans.
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Affiliation(s)
- Daniel Pfau
- Neuroscience Program, Michigan State University, Giltner Hall, 293 Farm Lane, Room 108, East Lansing, MI, 48824-1101, USA.
| | - Cynthia L Jordan
- Neuroscience Program, Michigan State University, Giltner Hall, 293 Farm Lane, Room 108, East Lansing, MI, 48824-1101, USA
| | - S Marc Breedlove
- Neuroscience Program, Michigan State University, Giltner Hall, 293 Farm Lane, Room 108, East Lansing, MI, 48824-1101, USA
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Leca JB, Gunst N, Shimizu K, Huffman MA, Takahata Y, Vasey PL. Hormonal contraceptive affects heterosexual but not homosexual behavior in free-ranging female Japanese macaques over 17 mating seasons. Horm Behav 2018; 105:166-176. [PMID: 30171829 DOI: 10.1016/j.yhbeh.2018.08.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/24/2018] [Revised: 08/18/2018] [Accepted: 08/24/2018] [Indexed: 11/25/2022]
Abstract
We assessed the effect of a progestin-based contraceptive treatment (chlormadinone acetate) on female heterosexual and homosexual behaviors in a free-ranging group of Japanese macaques (Macaca fuscata) living at Arashiyama-Kyoto, Central Japan. The data included estimated intensity of fertility cues, sexual solicitations and mounting behaviors collected daily during 17 consecutive mating seasons (1995-2012) from 159 females. Females that were on contraception: (1) exhibited less intense cues of putative fertility and for shorter periods; (2) were solicited by fewer males, and those males that did solicit them did so less often (i.e., lower heterosexual attractivity); (3) solicited fewer males and when they did perform sexual solicitations they did so less often (i.e., lower heterosexual proceptivity); (4) engaged in shorter heterosexual consortships with fewer male partners (i.e., lower heterosexual receptivity), compared with females that were not on contraception. In contrast, contraceptive treatment had no significant effect on the prevalence, occurrence, frequency, or duration of female homosexual behaviors. Even though heterosexual and homosexual behaviors can both be considered sexual in character and under hormonal control, our results suggested they are, to some extent, dissociable. Because females engaging in homosexual interactions showed less intense cues of putative fertility than those engaging in heterosexual interactions, regardless of contraceptive treatment, we argued that the hormonal threshold required for the expression of heterosexual behavior by females was associated with elevated sex hormones levels compared to homosexual behavior. We discussed the hormonal correlates of sexual behavior and partner preferences in Japanese macaques.
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Affiliation(s)
| | - Noëlle Gunst
- Department of Psychology, University of Lethbridge, Lethbridge, Japan
| | - Keiko Shimizu
- Department of Zoology, Okayama University of Science, Okayama, Japan
| | | | - Yukio Takahata
- School of Policy Studies, Kwansei Gakuin University, Sanda City, Japan
| | - Paul L Vasey
- Department of Psychology, University of Lethbridge, Lethbridge, Japan
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PAVLIČEV MIHAELA, WAGNER GÜNTER. The Evolutionary Origin of Female Orgasm. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2016; 326:326-337. [DOI: 10.1002/jez.b.22690] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2016] [Revised: 06/20/2016] [Accepted: 06/23/2016] [Indexed: 01/23/2023]
Affiliation(s)
- MIHAELA PAVLIČEV
- Center for Prevention of Preterm Birth; Perinatal Institute, Cincinnati Children's Hospital Medical Center; Cincinnati Ohio
- Department of Pediatrics; University of Cincinnati College of Medicine; Cincinnati Ohio
| | - GÜNTER WAGNER
- Department of Ecology and Evolutionary Biology; Yale University; New Haven Connecticut
- Yale Systems Biology Institute; Yale University; West Haven Connecticut
- Department of Obstetrics, Gynecology and Reproductive Sciences; Yale Medical School; New Haven Connecticut
- Department of Obstetrics and Gynecology; Wayne State University; Detroit Michigan
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Grueter CC, Stoinski TS. Homosexual Behavior in Female Mountain Gorillas: Reflection of Dominance, Affiliation, Reconciliation or Arousal? PLoS One 2016; 11:e0154185. [PMID: 27167861 PMCID: PMC4864209 DOI: 10.1371/journal.pone.0154185] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Accepted: 04/11/2016] [Indexed: 11/30/2022] Open
Abstract
Humans are unique among primates for not only engaging in same-sex sexual acts, but also forming homosexual pair bonds. To shed light on the evolutionary origins of homosexuality, data on the occurrence and contexts of same-sex behavior from nonhuman primates may be of particular significance. Homosexual behavior involving females is poorly researched in most primate taxa, exceptions being Japanese macaques, rhesus macaques, Hanuman langurs and bonobos. We present data on homosexual behavior in female mountain gorillas in the Virunga Volcanoes (Rwanda) and test four functional hypotheses, namely reconciliation, affiliation, dominance expression and sexual arousal. Homosexual interactions between females involved both ventro-dorsal and ventro-ventral copulations accompanied by vocalizations and courtship displays. The only sociosexual hypothesis that received partial empirical support is the social status hypothesis, i.e., that mounting reaffirms the dominance hierarchy. There is also some limited evidence that same-sex behavior reflects an overall state of arousal or is triggered via a 'pornographic' effect. An adaptive function of female homosexual behavior is not readily apparent, and we tentatively conclude (until a more rigorous test becomes available) that it may simply be related to sexual gratification or that it is an evolutionary by-product of an adaptation.
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Affiliation(s)
- Cyril C. Grueter
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley (Perth), WA, Australia
| | - Tara S. Stoinski
- The Dian Fossey Gorilla Fund International, SE Atlanta, Georgia, United States of America
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MacFarlane GR, Vasey PL. Promiscuous primates engage in same-sex genital interactions. Behav Processes 2016; 126:21-6. [PMID: 26930251 DOI: 10.1016/j.beproc.2016.02.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Revised: 01/26/2016] [Accepted: 02/24/2016] [Indexed: 10/22/2022]
Abstract
Same-sex genital interactions (SSGIs) occur across the order primates, yet explaining their maintenance in evolutionary terms appears problematic; as such interactions seem to counteract reproductive goals. We hypothesised that in more promiscuous species, where sexual motivation, mating effort, and non-conceptive heterosexual behaviour are greater, SSGIs may also occur at greater frequencies without necessarily impeding reproduction. We found that the expression of both male and female SSGIs were greater in multimale systems than in unimale ones. Both male and female SSGIs were positively correlated with the degree of promiscuity (relative testes mass). As mating system confers biases in the sex ratio that may influence the expression of SSGIs, we controlled for availability of members of the same-sex. When employing this control, results were largely congruent. For males, SSGIs were expressed more frequently in multimale systems. For both sexes, SSGIs were expressed more frequently with greater relative testes mass. We suggest SSGIs in primates may be a neutral by-product of selection for increases in promiscuous sexual activity, and that in certain instances these interactions may be co-opted to facilitate adaptive social functions.
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Affiliation(s)
- Geoff R MacFarlane
- School of Environmental and Life Sciences, University of Newcastle, Australia.
| | - Paul L Vasey
- Department of Psychology, University of Lethbridge, Canada
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8
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Faraut L, Northwood A, Majolo B. The functions of non-reproductive mounts among male Barbary macaques (Macaca sylvanus). Am J Primatol 2015. [PMID: 26204882 DOI: 10.1002/ajp.22451] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Same-sex, non-reproductive mounts have been observed in a number of primate species and in various social contexts. However, the function of non-reproductive mounts is still largely unknown. We aimed to test whether non-reproductive mounts function to assert dominance and as appeasement behavior in male Barbary macaques. We analyzed post-mount behavior in 54 macaques belonging to two captive groups at Trentham Monkey Forest in Staffordshire, using 10 min post-mount/matched-control focal sessions collected either on the mounter or the mountee. In support of the dominance assertion hypothesis, the higher-ranking male within a mounting pair was more likely to be the mounter than the mountee, and to mock bite the lower-ranking male. In support of the appeasement hypothesis, the former mounting partners were more likely to exchange grooming and to have a lower frequency of self-scratching (a measure of social tension) after a non-reproductive mount than in control sessions. Our study indicates that non-reproductive mounts have different and not mutually exclusive functions and can modulate the quality of social interactions among group members. We discuss the possible factors that can affect the occurrence of non-reproductive mounts within and between species.
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Affiliation(s)
- Lauriane Faraut
- School of Psychology, University of Lincoln, Lincoln, United Kingdom
| | - Amy Northwood
- School of Psychology, University of Lincoln, Lincoln, United Kingdom
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9
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Vasey PL, Leca JB, Gunst N, VanderLaan DP. Female homosexual behavior and inter-sexual mate competition in Japanese macaques: possible implications for sexual selection theory. Neurosci Biobehav Rev 2014; 46 Pt 4:573-8. [PMID: 25242104 DOI: 10.1016/j.neubiorev.2014.09.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Revised: 08/26/2014] [Accepted: 09/09/2014] [Indexed: 10/24/2022]
Abstract
In this paper, we review research related to female homosexual behavior in Japanese macaques (Macaca fuscata), including our 20-year program of research on this species. Multiple lines of evidence indicate that female homosexual behavior in this species is sexually motivated. In contrast, many sociosexual hypotheses have been tested in relation to female homosexual behavior in Japanese macaques, but none have been supported. Female Japanese macaques sometimes engage in same-sex sexual activity even when motivated opposite-sex alternatives are available. Within this context of mate choice, males compete inter-sexually for opportunities to copulate with females above and beyond any intra-sexual competition that is required. Anecdotal evidence suggests that inter-sexual competition for female sexual partners has been observed in a number of other species, including humans. At present it is unclear whether inter-sexual competition for sexual partners influences patterns of reproduction. Our understanding of sexual selection and the evolution of mating systems may be improved by investigating whether inter-sexual mate competition influences the acquisition and maintenance of reproductive partners in those species in which such interactions occur.
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Affiliation(s)
- Paul L Vasey
- Department of Psychology, University of Lethbridge, Lethbridge, Alberta T1K 3M4, Canada.
| | - Jean-Baptiste Leca
- Department of Psychology, University of Lethbridge, Lethbridge, Alberta T1K 3M4, Canada
| | - Noëlle Gunst
- Department of Psychology, University of Lethbridge, Lethbridge, Alberta T1K 3M4, Canada
| | - Doug P VanderLaan
- Gender Identity Service, Centre for Addiction and Mental Health, Toronto, Ontario M6J 1H4, Canada
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10
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Vasey PL, Chapais B, Gauthier C. Mounting Interactions between Female Japanese Macaques: Testing the Influence of Dominance and Aggression. Ethology 2010. [DOI: 10.1111/j.1439-0310.1998.tb00077.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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11
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Abstract
This paper presents a theoretical model for the evolution of same-sex sexual behavior, or homoerotic behavior, in humans. Contrary to the traditional study of the topic, the emphasis is on homoerotic behavior itself, irrespective of sexual orientation. It is an inferential model drawn from cross-species evidence, cross-cultural evidence, and current evolutionary theory. It is posited that humans evolved a disposition for homoerotic behavior because it increased same-sex affiliation among peripheralized hominids and indirectly influenced rates of survival and reproductive success. The implications for the conceptualization of same-sex sexual behavior and future research are indicated.
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Affiliation(s)
- F Muscarella
- Department of Psychology, Barry University, Miami Shores, FL 33161-6695, USA
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12
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Skewed sex ratios and female homosexual activity in Japanese macaques: An experimental analysis. Primates 2000; 41:17-25. [DOI: 10.1007/bf02557458] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/1999] [Accepted: 08/26/1999] [Indexed: 10/23/2022]
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13
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Abstract
The emerging field of evolutionary psychology provides fascinating new insights into many salient human behaviors, but homosexual behavior is not among these. The new field perpetuates old stereotypes, and useful evolutionary analysis of homosexual behavior is largely nonexistent. In this article, the treatment of homosexual behavior in the field of evolutionary psychology is reviewed, and the factors contributing to this treatment are identified. Recommendations are made to help foster the development of alternative evolutionary models of homosexual behavior.
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Affiliation(s)
- F Muscarella
- Department of Psychology, Barry University, Miami Shores, FL 33161-6695, USA
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15
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Michael RP, Zumpe D. A review of hormonal factors influencing the sexual and aggressive behavior of macaques. Am J Primatol 1993; 30:213-241. [PMID: 31937008 DOI: 10.1002/ajp.1350300306] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/1992] [Accepted: 02/09/1993] [Indexed: 11/11/2022]
Abstract
The effects of gonadal hormones on the sexual and aggressive behavior of adult macaques are reviewed. Similarities among findings from field, colony, and laboratory studies strengthen the view that testosterone facilitates the sexual and aggressive behavior of males, while sexual and perhaps aggressive behavior by the female is mainly dependent on estradiol, which increases both the sexual motivation of the female and her attractiveness to males. Differences between results from different settings help to emphasize the role of environmental and social factors in modulating the effects of hormones. © 1993 Wiley-Liss, Inc.
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Affiliation(s)
- Richard P Michael
- Department of Psychiatry and Behavioral Sciences, Emory University School of Medicine, Atlanta, Georgia
| | - Doris Zumpe
- Department of Psychiatry and Behavioral Sciences, Emory University School of Medicine, Atlanta, Georgia
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16
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Chapais B, Mignault C. Homosexual incest avoidance among females in captive Japanese macaques. Am J Primatol 1991; 23:171-183. [DOI: 10.1002/ajp.1350230304] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/1990] [Revised: 10/15/1990] [Indexed: 11/09/2022]
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17
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Mehlman PT, Chapais B. Differential effects of kinship, dominance, and the mating season on female allogrooming in a captive group ofMacaca fuscata. Primates 1988. [DOI: 10.1007/bf02381122] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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18
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Gouzoules H, Goy RW. Physiological and social influences on mounting behavior of troop-living female monkeys (Macaca fuscata). Am J Primatol 1983; 5:39-49. [DOI: 10.1002/ajp.1350050105] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/1983] [Accepted: 04/06/1983] [Indexed: 11/07/2022]
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19
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Allen ML, Lemmon WB. Orgasm in female primates. Am J Primatol 1981; 1:15-34. [DOI: 10.1002/ajp.1350010104] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/1980] [Accepted: 11/19/1980] [Indexed: 11/11/2022]
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20
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Goldfoot DA, Westerborg-van Loon H, Groeneveld W, Slob AK. Behavioral and physiological evidence of sexual climax in the female stump-tailed macaque (Macaca arctoides). Science 1980; 208:1477-9. [PMID: 7384791 DOI: 10.1126/science.7384791] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Intense tonic/clonic uterine contractions and sudden increases in heart rate coincided with the behavioral homolog of a male ejaculatory response (minus seminal emission) in a normal female stump-tailed macaque engaged in homosexual mounting episodes. The behavioral patterns were also observed in four of ten females during 5 to 40 percent of heterosexual copulations. These observations demonstrate the existence of an orgasmic response in a nonhuman primate.
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