Family size - homosexuality, gender dysphoria .
Fraternal birth order - homosexual feelings .
Fraternal birth order - homosexual feelings - men, women .
Male homosexuality & maternal fecundity .
.. PubMed search ..
Tuesday, March 31, 2009
Wednesday, March 11, 2009
Fraternal birth order - homosexual feelings - men, women
Fraternal birth order and ratio of heterosexual/homosexual feelings in women and men.
J Homosex. 2006;51(4):161-74.
McConaghy N, Hadzi-Pavlovic D, Stevens C, Manicavasagar V, Buhrich N, Vollmer-Conna U.
Studies of the 2-3% of persons who identify as homosexual found men but not women had more older brothers than persons who identify as heterosexual. The present study investigated the birth order in the approximately 20% of men and women who anonymously report some homosexual feelings, few of whom identify as homosexual. The number of older brothers and sisters was investigated in seven cohorts: 319 male twins; and 49, 54, and 61 female and 66, 116, and 50 male medical students. Both women and men who anonymously reported homosexual feelings had a greater mean number of older brothers and sisters than did those who reported no homosexual feelings. The difference was stronger in relation to brothers than sisters. The birth order effect was not related to the strength of the subjects' degree of homosexual compared with heterosexual feelings. Its presence in women could not be accounted for by the widely accepted hypothesis that the birth order effect is due to a maternal immune reaction provoked only by male fetuses. The lack of relationship between the strength of the effect and degree of homosexual feelings in the men and women suggests the influence of birth order on homosexual feelings was not due to a biological, but a social process in the subjects studied. Investigating the neglected significant percentage of predominantly heterosexual men and women who anonymously report some homosexual feelings may aid in understanding the factors influencing sexual orientation, and identity.
University of New South Wales, New South Wales, Australia.
J Homosex. 2006;51(4):161-74.
McConaghy N, Hadzi-Pavlovic D, Stevens C, Manicavasagar V, Buhrich N, Vollmer-Conna U.
Studies of the 2-3% of persons who identify as homosexual found men but not women had more older brothers than persons who identify as heterosexual. The present study investigated the birth order in the approximately 20% of men and women who anonymously report some homosexual feelings, few of whom identify as homosexual. The number of older brothers and sisters was investigated in seven cohorts: 319 male twins; and 49, 54, and 61 female and 66, 116, and 50 male medical students. Both women and men who anonymously reported homosexual feelings had a greater mean number of older brothers and sisters than did those who reported no homosexual feelings. The difference was stronger in relation to brothers than sisters. The birth order effect was not related to the strength of the subjects' degree of homosexual compared with heterosexual feelings. Its presence in women could not be accounted for by the widely accepted hypothesis that the birth order effect is due to a maternal immune reaction provoked only by male fetuses. The lack of relationship between the strength of the effect and degree of homosexual feelings in the men and women suggests the influence of birth order on homosexual feelings was not due to a biological, but a social process in the subjects studied. Investigating the neglected significant percentage of predominantly heterosexual men and women who anonymously report some homosexual feelings may aid in understanding the factors influencing sexual orientation, and identity.
University of New South Wales, New South Wales, Australia.
Monday, March 9, 2009
Paraphilia - Males
Neurodevelopmental correlates of paraphilic sexual interests in men.
Arch Sex Behav. 2008 Feb;37(1):166-72.
Rahman Q, Symeonides DJ.
The etiology of anomalous, or paraphilic, sexual preferences in men is unclear although a growing literature points to their prenatal neurodevelopmental ontogenesis. The present study explored whether this was also apparent in a community sample of 200 heterosexual men by examining their sexual fantasies using the Wilson Sex Fantasy Questionnaire (WSFQ) and several demographic and somatic neurodevelopmental markers, including sibling sex composition, handedness, maternal and paternal age at birth, second to fourth finger length ratios, and fluctuating asymmetry of finger lengths and wrist widths. Responses to the WSFQ were used to quantify the extent of paraphilic interest by computing a variance-quotient (or VQ) previously shown to differentiate paraphilic from conventional heterosexual males. High paraphilic scorers had a significantly greater number of older brothers, higher right-hand 2D:4D, and a trend for lower Edinburgh Handedness Inventory (EHI) scores compared to low-paraphilic scorers. Correlational analysis revealed a significant positive association of VQ scores with number of older brothers and significant negative associations with number of younger brothers and EHI scores (elevated paraphilic interests were correlated with elevated non-right handedness). Correlations between VQ scores and other variables were not significant. It is suggested that processes such as developmental instability and maternal immunity may play a role in variant sexual preferences among otherwise healthy heterosexual men.
Department of Biological Sciences, Queen Mary College, University of London, Mile End Road, London, UK. q.rahman@qmul.ac.uk
Arch Sex Behav. 2008 Feb;37(1):166-72.
Rahman Q, Symeonides DJ.
The etiology of anomalous, or paraphilic, sexual preferences in men is unclear although a growing literature points to their prenatal neurodevelopmental ontogenesis. The present study explored whether this was also apparent in a community sample of 200 heterosexual men by examining their sexual fantasies using the Wilson Sex Fantasy Questionnaire (WSFQ) and several demographic and somatic neurodevelopmental markers, including sibling sex composition, handedness, maternal and paternal age at birth, second to fourth finger length ratios, and fluctuating asymmetry of finger lengths and wrist widths. Responses to the WSFQ were used to quantify the extent of paraphilic interest by computing a variance-quotient (or VQ) previously shown to differentiate paraphilic from conventional heterosexual males. High paraphilic scorers had a significantly greater number of older brothers, higher right-hand 2D:4D, and a trend for lower Edinburgh Handedness Inventory (EHI) scores compared to low-paraphilic scorers. Correlational analysis revealed a significant positive association of VQ scores with number of older brothers and significant negative associations with number of younger brothers and EHI scores (elevated paraphilic interests were correlated with elevated non-right handedness). Correlations between VQ scores and other variables were not significant. It is suggested that processes such as developmental instability and maternal immunity may play a role in variant sexual preferences among otherwise healthy heterosexual men.
Department of Biological Sciences, Queen Mary College, University of London, Mile End Road, London, UK. q.rahman@qmul.ac.uk
Tuesday, March 3, 2009
Male homosexuality & maternal fecundity
New evidence of genetic factors influencing sexual orientation in men: female fecundity increase in the maternal line.
Arch Sex Behav. 2009 Jun;38(3):393-9. Epub 2008 Jun 17.
Iemmola F, Camperio Ciani A.
There is a long-standing debate on the role of genetic factors influencing homosexuality because the presence of these factors contradicts the Darwinian prediction according to which natural selection should progressively eliminate the factors that reduce individual fecundity and fitness. Recently, however, Camperio Ciani, Corna, and Capiluppi (Proceedings of the Royal Society of London, Series B: Biological Sciences, 271, 2217-2221, 2004), comparing the family trees of homosexuals with heterosexuals, reported a significant increase in fecundity in the females related to the homosexual probands from the maternal line but not in those related from the paternal one. This suggested that genetic factors that are partly linked to the X-chromosome and that influence homosexual orientation in males are not selected against because they increase fecundity in female carriers, thus offering a solution to the Darwinian paradox and an explanation of why natural selection does not progressively eliminate homosexuals. Since then, new data have emerged suggesting not only an increase in maternal fecundity but also larger paternal family sizes for homosexuals. These results are partly conflicting and indicate the need for a replication on a wider sample with a larger geographic distribution. This study examined the family trees of 250 male probands, of which 152 were homosexuals. The results confirmed the study of Camperio Ciani et al. (2004). We observed a significant fecundity increase even in primiparous mothers, which was not evident in the previous study. No evidence of increased paternal fecundity was found; thus, our data confirmed a sexually antagonistic inheritance partly linked to the X-chromosome that promotes fecundity in females and a homosexual sexual orientation in males.
Department of General Psychology, University of Padova, via Belzoni 80, Padua, Italy.
Evidence for maternally inherited factors favouring male homosexuality and promoting female fecundity.
Proc Biol Sci. 2004 Nov 7;271(1554):2217-21.
Camperio-Ciani A, Corna F, Capiluppi C.
The Darwinian paradox of male homosexuality in humans is examined, i.e. if male homosexuality has a genetic component and homosexuals reproduce less than heterosexuals, then why is this trait maintained in the population? In a sample of 98 homosexual and 100 heterosexual men and their relatives (a total of over 4600 individuals), we found that female maternal relatives of homosexuals have higher fecundity than female maternal relatives of heterosexuals and that this difference is not found in female paternal relatives. The study confirms previous reports, in particular that homosexuals have more maternal than paternal male homosexual relatives, that homosexual males are more often later-born than first-born and that they have more older brothers than older sisters. We discuss the findings and their implications for current research on male homosexuality.
Department of General Psychology, Università di Padova, via Venezia 8, 35100 Padua, Italy. andrea.camperio@unipd.it
Arch Sex Behav. 2009 Jun;38(3):393-9. Epub 2008 Jun 17.
Iemmola F, Camperio Ciani A.
There is a long-standing debate on the role of genetic factors influencing homosexuality because the presence of these factors contradicts the Darwinian prediction according to which natural selection should progressively eliminate the factors that reduce individual fecundity and fitness. Recently, however, Camperio Ciani, Corna, and Capiluppi (Proceedings of the Royal Society of London, Series B: Biological Sciences, 271, 2217-2221, 2004), comparing the family trees of homosexuals with heterosexuals, reported a significant increase in fecundity in the females related to the homosexual probands from the maternal line but not in those related from the paternal one. This suggested that genetic factors that are partly linked to the X-chromosome and that influence homosexual orientation in males are not selected against because they increase fecundity in female carriers, thus offering a solution to the Darwinian paradox and an explanation of why natural selection does not progressively eliminate homosexuals. Since then, new data have emerged suggesting not only an increase in maternal fecundity but also larger paternal family sizes for homosexuals. These results are partly conflicting and indicate the need for a replication on a wider sample with a larger geographic distribution. This study examined the family trees of 250 male probands, of which 152 were homosexuals. The results confirmed the study of Camperio Ciani et al. (2004). We observed a significant fecundity increase even in primiparous mothers, which was not evident in the previous study. No evidence of increased paternal fecundity was found; thus, our data confirmed a sexually antagonistic inheritance partly linked to the X-chromosome that promotes fecundity in females and a homosexual sexual orientation in males.
Department of General Psychology, University of Padova, via Belzoni 80, Padua, Italy.
Evidence for maternally inherited factors favouring male homosexuality and promoting female fecundity.
Proc Biol Sci. 2004 Nov 7;271(1554):2217-21.
Camperio-Ciani A, Corna F, Capiluppi C.
The Darwinian paradox of male homosexuality in humans is examined, i.e. if male homosexuality has a genetic component and homosexuals reproduce less than heterosexuals, then why is this trait maintained in the population? In a sample of 98 homosexual and 100 heterosexual men and their relatives (a total of over 4600 individuals), we found that female maternal relatives of homosexuals have higher fecundity than female maternal relatives of heterosexuals and that this difference is not found in female paternal relatives. The study confirms previous reports, in particular that homosexuals have more maternal than paternal male homosexual relatives, that homosexual males are more often later-born than first-born and that they have more older brothers than older sisters. We discuss the findings and their implications for current research on male homosexuality.
Department of General Psychology, Università di Padova, via Venezia 8, 35100 Padua, Italy. andrea.camperio@unipd.it
Sunday, March 1, 2009
Fraternal birth order - homosexual feelings
Fraternal birth order and ratio of heterosexual/homosexual feelings in women and men.
J Homosex. 2006;51(4):161-74.
McConaghy N, Hadzi-Pavlovic D, Stevens C, Manicavasagar V, Buhrich N, Vollmer-Conna U.
Studies of the 2-3% of persons who identify as homosexual found men but not women had more older brothers than persons who identify as heterosexual.
The present study investigated the birth order in the approximately 20% of men and women who anonymously report some homosexual feelings, few of whom identify as homosexual. The number of older brothers and sisters was investigated in seven cohorts: 319 male twins; and 49, 54, and 61 female and 66, 116, and 50 male medical students. Both women and men who anonymously reported homosexual feelings had a greater mean number of older brothers and sisters than did those who reported no homosexual feelings. The difference was stronger in relation to brothers than sisters. The birth order effect was not related to the strength of the subjects' degree of homosexual compared with heterosexual feelings. Its presence in women could not be accounted for by the widely accepted hypothesis that the birth order effect is due to a maternal immune reaction provoked only by male fetuses. The lack of relationship between the strength of the effect and degree of homosexual feelings in the men and women suggests the influence of birth order on homosexual feelings was not due to a biological, but a social process in the subjects studied. Investigating the neglected significant percentage of predominantly heterosexual men and women who anonymously report some homosexual feelings may aid in understanding the factors influencing sexual orientation, and identity.
University of New South Wales, New South Wales, Australia.
J Homosex. 2006;51(4):161-74.
McConaghy N, Hadzi-Pavlovic D, Stevens C, Manicavasagar V, Buhrich N, Vollmer-Conna U.
Studies of the 2-3% of persons who identify as homosexual found men but not women had more older brothers than persons who identify as heterosexual.
The present study investigated the birth order in the approximately 20% of men and women who anonymously report some homosexual feelings, few of whom identify as homosexual. The number of older brothers and sisters was investigated in seven cohorts: 319 male twins; and 49, 54, and 61 female and 66, 116, and 50 male medical students. Both women and men who anonymously reported homosexual feelings had a greater mean number of older brothers and sisters than did those who reported no homosexual feelings. The difference was stronger in relation to brothers than sisters. The birth order effect was not related to the strength of the subjects' degree of homosexual compared with heterosexual feelings. Its presence in women could not be accounted for by the widely accepted hypothesis that the birth order effect is due to a maternal immune reaction provoked only by male fetuses. The lack of relationship between the strength of the effect and degree of homosexual feelings in the men and women suggests the influence of birth order on homosexual feelings was not due to a biological, but a social process in the subjects studied. Investigating the neglected significant percentage of predominantly heterosexual men and women who anonymously report some homosexual feelings may aid in understanding the factors influencing sexual orientation, and identity.
University of New South Wales, New South Wales, Australia.
Family size - homosexuality, gender dysphoria
Sibship size, sibling sex ratio, birth order, and parental age in homosexual and nonhomosexual gender dysphorics.
J Nerv Ment Dis. 1992 Jan;180(1):40-7.
Blanchard R, Sheridan PM.
This study investigated whether demographic variables previously reported to differentiate ordinary homosexuals from heterosexuals also differentiate gender-dysphoric homosexuals from gender-dysphoric persons with other sexual orientations. Subjects were outpatients aged 16 and older who were referred by physicians to a specialty clinic for the assessment of gender identity disorders. The subjects were divided into three groups: 204 homosexual women, 193 homosexual men, and 273 nonhomosexual men; the last category included men sexually attracted to females, to both sexes, and to neither sex. Demographic data on patients' families of origin were extracted from their clinical charts and from structured interview protocols. A multiple-range test at the .05 level showed that the homosexual men had significantly more siblings than the homosexual women, who, in turn, had significantly more siblings than the nonhomosexual men. The sibling sex ratio of the homosexual men, 131 brothers per 100 sisters, was significantly higher than the sex ratio of live births for the population as a whole (106 men per 100 women; p = .01); the sibling sex ratios of the other groups did not differ from the expected value. The homosexual men had a significantly later birth order than the nonhomosexual men (p = .004); the homosexual women, who fell in between, did not differ significantly from either male group. There were no between-groups differences in paternal or maternal age at the time of the subject's birth. The results concerning sibling sex ratio and birth order are consistent with previous findings for homosexual men.
Gender Identity Clinic, Clarke Institute of Psychiatry, Toronto, Ontario, Canada.
J Nerv Ment Dis. 1992 Jan;180(1):40-7.
Blanchard R, Sheridan PM.
This study investigated whether demographic variables previously reported to differentiate ordinary homosexuals from heterosexuals also differentiate gender-dysphoric homosexuals from gender-dysphoric persons with other sexual orientations. Subjects were outpatients aged 16 and older who were referred by physicians to a specialty clinic for the assessment of gender identity disorders. The subjects were divided into three groups: 204 homosexual women, 193 homosexual men, and 273 nonhomosexual men; the last category included men sexually attracted to females, to both sexes, and to neither sex. Demographic data on patients' families of origin were extracted from their clinical charts and from structured interview protocols. A multiple-range test at the .05 level showed that the homosexual men had significantly more siblings than the homosexual women, who, in turn, had significantly more siblings than the nonhomosexual men. The sibling sex ratio of the homosexual men, 131 brothers per 100 sisters, was significantly higher than the sex ratio of live births for the population as a whole (106 men per 100 women; p = .01); the sibling sex ratios of the other groups did not differ from the expected value. The homosexual men had a significantly later birth order than the nonhomosexual men (p = .004); the homosexual women, who fell in between, did not differ significantly from either male group. There were no between-groups differences in paternal or maternal age at the time of the subject's birth. The results concerning sibling sex ratio and birth order are consistent with previous findings for homosexual men.
Gender Identity Clinic, Clarke Institute of Psychiatry, Toronto, Ontario, Canada.
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