Birth Order in Homosexual Versus Heterosexual Sex Offenders Against Children, Pubescents, and Adults

Homosexual men erotically attracted to physically mature partners typically have more older brothers than comparable heterosexual men. We investigated whether late fraternal birth positions also occur in homosexuals attracted to children or pubescents. Probands were 710 sex offenders from Gebhard et al.'s (1965) study of sexual offending. Homosexual offenders against adults and pubescents had later fraternal birth positions than heterosexual offenders against adults and pubescents, respectively; there was no difference between the homosexual and heterosexual offenders against children. Results provide some evidence that homosexuality in men attracted to immature males is etiologically related to homosexuality in men attracted to mature males.     

Birth Order in Sex-Offending and Aggressive-Offending Men

The relation between birth order and number of sexual and violent convictions was investigated retrospectively in a sample of 113 men, to determine whether the established fraternal birth order effect in male homosexual preference and deviant sexual preference (e.g., for rape and pedophilia) may be extended to sexual behavior. Participants were mentally disordered offenders detained in a medium secure psychiatric unit in the United Kingdom and comprised 64 men with sexual convictions and 49 men with nonsexual violent convictions. Sibling data from psychiatric notes were used to calculate Berglin's birth order index for each participant and conviction data were obtained from the Home Office Offenders' Index. Fraternal birth order was significantly correlated with number of sexual convictions (p ≤ .05). No association was found between fraternal or sororal birth order and violent convictions in either the sex offender or violent offender group. Results suggest that the fraternal birth order effect previously found for deviant sexual preference in sex offenders (K. Côté, C. M. Earls, &; M. L. Lalumière, 2002; M. L. Lalumière, G. T. Harris, V. L. Quinsey, &; M. E. Rice, 1998) also applies to sexually deviant behavior and is specific to sexual rather than general offending. Results are discussed in terms of the maternal immunosensitization hypothesis.     

Does sexual abuse in childhood cause pedophilia: An exploratory study

The reliability of the notion that pedophilia is caused by sexual abuse in childhood was explored by examining retrospective self-reports of 344 males. Included in the study were 77 heterosexual pedophiles, 54 homosexual pedophiles, 51 nonpedophilic sex offenders against children, 36 sex offenders against physically mature females, 75 heterosexual paid volunteers who erotically preferred mature females, and 51 homosexual clients who preferred mature males. For each sex offender the differential diagnosis of an erotic preference for minors vs. a preference for physically mature partners was made by means of the phallometric test of erotic gender and age preferences. The analysis of self-reports confirmed that the proportion of pedophiles who report having been sexually abused in childhood by mature persons is larger than that of men who were not charged for or accused of a sex offense against a child though the difference is relatively small (28.6 vs. 13.9 and 10.7% for the heterosexual pedophiles and the two groups of gynephiles, respectively, and 25.9 vs. 11.8% for the homosexual pedophiles and androphiles, respectively). Further analysis demonstrated, however, that pedophiles who admitted having an erotic interest in children significantly more often claimed that they had been sexually abused as children than pedophiles who did not admit having such feelings. This interdependence renders the reliability of these self-reports questionable.This research was supported in part by grant MA-9134 from the Medical Research Council of Canada.Forensic Division Clarke Institute of Psychiatry     

How Many Gay Men Owe Their Sexual Orientation to Fraternal Birth Order?

In men, sexual orientation correlates with the number of older brothers, each additional older brother increasing the odds of homosexuality by approximately 33%. However, this phenomenon, the fraternal birth order effect, accounts for the sexual orientation of only a proportion of gay men. To estimate the size of this proportion, we derived generalized forms of two epidemiological statistics, the attributable fraction and the population attributable fraction, which quantify the relationship between a condition and prior exposure to an agent that can cause it. In their common forms, these statistics are calculable only for 2 levels of exposure: exposed versus not-exposed. We developed a method applicable to agents with multiple levels of exposure—in this case, number of older brothers. This noniterative method, which requires the odds ratio from a prior logistic regression analysis, was then applied to a large contemporary sample of gay men. The results showed that roughly 1 gay man in 7 owes his sexual orientation to the fraternal birth order effect. They also showed that the effect of fraternal birth order would exceed all other causes of homosexuality in groups of gay men with 3 or more older brothers and would precisely equal all other causes in a theoretical group with 2.5 older brothers. Implications are suggested for the gay sib-pair linkage method of identifying genetic loci for homosexuality.     

Sibling Sex Ratio and Sexual Orientation in Men and Women: New Tests in Two National Probability Samples

One line of research on the etiology of sexual orientation has examined sibling sex ratio, the ratio of brothers to sisters collectively reported by a group of individuals, but this research has only used clinical and/or convenience samples. In the present study, homosexual men and women’s sibling sex ratio was examined in two national probability samples. Results indicated that homosexual men had a sex ratio of 129.54 male live births to 100 female live births. This ratio was within the range of elevated sex ratios found in some previous studies of homosexual men, although it was only marginally significant (p = .09) relative to the known human sex ratio with regard to live births. Additional analyses indicated that this effect was likely the result of a high fraternal birth order (i.e., an elevated number of older brothers) in homosexual men. The sibling sex ratio for lesbians was 122.58 male live births to 100 female live births, which did not significantly differ from the known human sex ratio with regard to live births. The results for lesbians, however, should be interpreted with caution because the sample size (and resulting power) was low. The results in men add to research suggesting that homosexual men, unselected for gender identity or gender role behavior, do not have elevated sibling sex ratios. These results also suggest that research should concentrate on finding the cause(s) of the fraternal birth order effect, the consistent finding that homosexual men have an elevated number of older brothers.     

Birth Order,Sibling Sex Ratio,Handedness, and Sexual Orientation of Male and Female Participants in a BBC Internet Research Project

This study investigated the relations among sexual orientation, fraternal birth order (number of older brothers), and hand-preference. The participants were 87,798 men and 71,981 women who took part in a Web-based research project sponsored by the British Broadcasting Corporation (BBC). The results yielded some evidence confirming prior findings that non-right-handedness is associated with homosexuality in men and women, that older brothers increase the odds of homosexuality in men, and that the effect of older brothers on sexual orientation is limited to right-handed men. The evidence was weaker than in previous studies, however, probably because the usual relations among the variables of interest were partially obscured by the effects of other factors. Thus, the homosexual men and women had higher rates of non-right-handedness than their heterosexual counterparts, but the strongest handedness finding for both sexes was a marked tendency for participants who described themselves as ambidextrous also to describe themselves as bisexual. The birth order data were strongly affected by a tendency for the male participants to report an excess of older sisters, and the female participants to report an excess of older brothers. Statistical analyses confirmed that this was an artifact of the parental stopping rule, “Continue having children until you have offspring of both sexes.” In subsequent analyses, participants were divided into those who did and did not have younger siblings, on the grounds that the data of the former would be less contaminated by the stopping rule. In the former subsample, the right-handed homo/bisexual males showed the typical high ratio of older brothers to older sisters, whereas the non-right-handed homo/bisexual males did not.     

Detecting and Correcting for Family Size Differences in the Study of Sexual Orientation and Fraternal Birth Order

The term “fraternal birth order effect” denotes a statistical relation most commonly expressed in one of two ways: Older brothers increase the odds of homosexuality in later born males or, alternatively, homosexual men tend to have more older brothers than do heterosexual men. The demonstrability of this effect depends partly on the adequate matching of the homosexual and heterosexual study groups with respect to mean family size. If the homosexual group has too many siblings, relative to the heterosexual group, the homosexual group will tend to show the expected excess of older brothers but may also show an excess of other sibling-types (most likely older sisters); if the homosexual group has too few siblings, it will tend not to show a difference in number of older brothers but instead may show a deficiency of other sibling-types (most likely younger brothers and younger sisters). In the first part of this article, these consequences are illustrated with deliberately mismatched groups selected from archived data sets. In the second part, two slightly different methods for transforming raw sibling data are presented. These are intended to produce family-size-corrected variables for each of the four original sibling parameters (older brothers, older sisters, younger brothers, and younger sisters). Both versions are shown to render the fraternal birth order effect observable in the deliberately mismatched groups. In the third part of the article, fraternal birth order studies published in the last 5 years were surveyed for failures to find a statistically significant excess of older brothers for the homosexual group. Two such studies were found in the nine examined. In both cases, the collective findings for older sisters, younger brothers, and younger sisters suggested that the mean family size of the homosexual groups was smaller than that of the heterosexual comparison groups. Furthermore, the individual findings for the four classes of siblings resembled those for the present experimentally mismatched groups in which the mean family size of the homosexual group was significantly smaller. This illustrates the necessity of comparing groups on measures of mean family size and removing this confound in some way when those means are markedly different.     

Fraternal Birth Order,Family Size,and Male Homosexuality: Meta-Analysis of Studies Spanning 25 Years

The fraternal birth order effect is the tendency for older brothers to increase the odds of homosexuality in later-born males. This study compared the strength of the effect in subjects from small versus large families and in homosexual subjects with masculine versus feminine gender identities. Meta-analyses were conducted on 30 homosexual and 30 heterosexual groups from 26 studies, totaling 7140 homosexual and 12,837 heterosexual males. The magnitude of the fraternal birth order effect was measured with a novel variable, the Older Brothers Odds Ratio, computed as (homosexuals’ older brothers ÷ homosexuals’ other siblings) ÷ (heterosexuals’ older brothers ÷ heterosexuals’ other siblings), where other siblings = older sisters + younger brothers + younger sisters. An Older Brothers Odds Ratio of 1.00 represents no effect of sexual orientation; values over 1.00 are positive evidence for the fraternal birth order effect. Evidence for the reliability of the effect was consistent. The Older Brothers Odds Ratio was significantly >1.00 in 20 instances, >1.00 although not significantly in nine instances, and nonsignificantly <1.00 in 1 instance. The pooled Older Brothers Odds Ratio for all samples was 1.47, p < .00001. Subgroups analyses showed that the magnitude of the effect was significantly greater in the 12 feminine or transgender homosexual groups than in the other 18 homosexual groups. There was no evidence that the magnitude of the effect differs according to family size.     

Birth Order and Sibling Sex Ratio in Homosexual and Heterosexual Non-White Men

Researchers interested in the development of sexual orientation have investigated predominantly or exclusively White samples. To address this imbalance, the relations between sexual orientation and two biodemographic variables, birth order and sibling sex ratio, were examined in a sample of non-White men. The men (N = 823) were interviewed by investigators at the Kinsey Institute for Sex and Reproduction from 1938 to 1963. A significantly later birth order was observed for non-White homosexual men relative to non-White heterosexual men. Non-White homosexual men also had an elevated sibling sexratio. Results add to the generalizabilityof the birth order and sibling sex ratio effects previously observed to occur in (White) homosexual men.     

Birth order and sibling sex ratio in two samples of Dutch gender-dysphoric homosexual males

Two studies were undertaken to confirm the previous findings that homosexual men in general tend to have a later than expected birth order and that extremely feminine homosexual men also tend to have a higher than expected proportion of brothers (i.e. a highersibling sex ratio). Subjects in Study 1 were Dutch, adult and adolescent, biological male patients with gender dysphoria (persistent and recurrent desires to belong to the opposite sex), who were undergoing treatment with feminizing hormones. These comprised 83 patients who reported sexual attraction to other males (the homosexual group) and 58 who reported sexual attraction to females or equal attraction to males and females (the nonhomosexual group). Subjects in Study 2 were Dutch adolescent male patients at another hospital. The homosexual group consisted of 21 gender-dysphoric homosexual teenagers referred to a gender identity clinic for children and adolescents. The control group were 21 adolescent males referred to the child psychiatry department of the same hospital for reasons other than gender identity disorder, homosexuality, or transvestism. These were individually matched to the homosexual subjects on age and sibship size. In both studies, the homosexual group had a significantly later average birth order than the comparison group. In Study 1, the homosexual group had a significantly elevated sibling sex ratio; this was not tested in Study 2 because of its small sample size. These studies add to the mounting evidence that late birth orders are common to all homosexual samples and that elevated sibling sex ratios are an additional characteristic of extremely feminine ones.     

Pedophilia and heterosexuality vs. homosexuality

In the context of a search for testable etiological theories of pedophilia, the relationship of pedophilia to partner sex preference was investigated. The proportional prevalences of gynephilia and androphilia were compared with the proportional prevalences of sexual offenders victimizing female children and of such offenders against male children. Since pedophilia either does not exist at all in women, or is extremely rare, only men were included in the study. We derived the proportional prevalence of androphilia from a review of the main pertinent studies, including Gebhard's reassessment of the study by Kinsey et al. particularly of the section on gynephilia vs. androphilia. The numbers of heterosexual vs. homosexual offenders against children were derived from the studies by Mohr et al., by Gebhard et al., and from a group of 457 sex offenders against children seen in the course of several years at the Department of Behavioural Sexology of the Clarke Institute of Psychiatry. There was a large difference between the proportion of prevalences of heterosexual vs. homosexual offenders against children on the one hand and the proportional prevalences of gynephilia vs. androphilia, on the other. This difference suggests that the development of erotically preferred partner sex and partner age are not independent of each other and that in pedophilia, the development of heterosexuality or homosexuality is brought about by factors different from those operative in the development of androphilia or gynephilia.     

Biodemographic and Physical Correlates of Sexual Orientation in Men

To better understand sexual orientation from an evolutionary perspective, we investigated whether, compared to heterosexual men, the fewer direct descendants of homosexual men could be counterbalanced by a larger number of other close biological relatives. We also investigated the extent to which three patterns generally studied separately––handedness, number of biological older brothers, and hair-whorl rotation pattern––correlated with each other, and for evidence of replication of previous findings on how each pattern related to sexual orientation. We surveyed at Gay Pride and general community festivals, analyzing data for 894 heterosexual men and 694 homosexual men, both groups predominantly (~80%) white/non-Hispanic. The Kinsey distribution of sexual orientation for men recruited from the general community festivals approximated previous population-based surveys. Compared to heterosexual men, homosexual men had both more relatives, especially paternal relatives, and more homosexual male relatives. We found that the familiality for male sexual orientation decreased with relatedness, i.e., when moving from first-degree to second-degree relatives. We also replicated the fraternal birth order effect. However, we found no significant correlations among handedness, hair whorl rotation pattern, and sexual orientation, and, contrary to some previous research, no evidence that male sexual orientation is transmitted predominantly through the maternal line.     

Older-Sibling and Younger-Sibling Sex Ratios in Frisch and Hviid’s (2006) National Cohort Study of Two Million Danes

Frisch and Hviid (2006) recently reported a study of variables that predicted heterosexual and homosexual marriage in a national cohort of Danish men and women. They found no evidence that older brothers increase the probability that a man will legally marry another man. They concluded that their data raise questions about the universality of the widely confirmed finding that older brothers increase the probability that a man will be sexually oriented towards other men (the fraternal birth order effect). In the present article, Frisch and Hviid’s data were reanalyzed using one of the procedures that have been used in prior studies of fraternal birth order. The results showed that the sex ratio of older brothers to older sisters was significantly higher than the expected value of 106 in all four of their study groups (heterosexually married men, homosexually married men, heterosexually married women, and homosexually married women). In contrast, the sex ratio of younger brothers to younger sisters approximated 106 in all four groups. According to this analysis, the only group whose data resembled data from previous studies was the homosexually married males. The writer concluded that one cannot interpret findings about the correlates of heterosexual and homosexual marriage as if they were findings about the correlates of heterosexual and homosexual orientation, and that this is underscored by comparing the markedly different older-sibling sex ratios obtained from heterosexually married persons (in the Danish study) and those obtained from heterosexually oriented persons (in previous studies). It is unclear what implications, if any, Frisch and Hviid’s findings have for the study of sexual orientation in general.     

Older-sibling and younger-sibling sex ratios in Frisch and Hviid's (2006) national cohort study of two million Danes

Frisch and Hviid (2006) recently reported a study of variables that predicted heterosexual and homosexual marriage in a national cohort of Danish men and women. They found no evidence that older brothers increase the probability that a man will legally marry another man. They concluded that their data raise questions about the universality of the widely confirmed finding that older brothers increase the probability that a man will be sexually oriented towards other men (the fraternal birth order effect). In the present article, Frisch and Hviid's data were reanalyzed using one of the procedures that have been used in prior studies of fraternal birth order. The results showed that the sex ratio of older brothers to older sisters was significantly higher than the expected value of 106 in all four of their study groups (heterosexually married men, homosexually married men, heterosexually married women, and homosexually married women). In contrast, the sex ratio of younger brothers to younger sisters approximated 106 in all four groups. According to this analysis, the only group whose data resembled data from previous studies was the homosexually married males. The writer concluded that one cannot interpret findings about the correlates of heterosexual and homosexual marriage as if they were findings about the correlates of heterosexual and homosexual orientation, and that this is underscored by comparing the markedly different older-sibling sex ratios obtained from heterosexually married persons (in the Danish study) and those obtained from heterosexually oriented persons (in previous studies). It is unclear what implications, if any, Frisch and Hviid's findings have for the study of sexual orientation in general.     

Deficient erotic gender differentiation in pedophilia: A follow-up

Divided 262 phallometrically diagnosed pedophiles into heterosexual, homosexual, and bisexual groups, according to the sex of their victims. Each group was then divided into 3 subgroups according to degree of admitting to an erotic preference for children. They were compared among each other and with 47 self-professed heterosexual and 20 self-professed homosexual male volunteers phallometrically diagnosed as having an erotic preference for physically mature partners. The comparison was in regard to phallometrically assessed erotic gender differentiation. Results demonstrate that gender differentiation of even the fully admitting heterosexual pedophiles was significantly weaker than that of the heterosexual controls, and the gender differentiation of the fully admitting homosexual pedophiles was significantly weaker than that of both groups of controls. Gender differentiation of the nonadmitting heterosexual pedophiles was significantly weaker than that of the heterosexual pedophiles who fully admitted to their paraphilia. This was demonstrated to be caused by the nonadmitters suppression of responses.     

The proportions of heterosexual and homosexual pedophiles among sex offenders against children: an exploratory study.

Previous investigations have indicated that the ratio of sex offenders against female children vs. offenders against male children is approximately 2:1, while the ratio of gynephiles to androphiles among the general population is approximately 20:1. The present study investigated whether the etiology of preferred partner sex among pedophiles is related to the etiology of preferred partner sex among males preferring adult partners. Using phallometric test sensitivities to calculate the proportion of true pedophiles among various groups of sex offenders against children, and taking into consideration previously reported mean numbers of victims per offender group, the ratio of heterosexual to homosexual pedophiles was calculated to be approximately 11:1. This suggests that the resulting proportion of true pedophiles among persons with a homosexual erotic development is greater than that in persons who develop heterosexually. This, of course, would not indicate that androphilic males have a greater propensity to offend against children.     

Is Homosexuality a Paraphilia? The Evidence For and Against

Whether homosexuality should be described as one among many paraphilic sexual interests or an altogether different dimension of sexual interest has long been discussed in terms of its political and social implications. The present article examined the question instead by comparing the major correlates and other features of homosexuality and of the paraphilias, including prevalence, sex ratio, onset and course, fraternal birth order, physical height, handedness, IQ and cognitive neuropsychological profile, and neuroanatomy. Although those literatures remain underdeveloped, the existing findings thus far suggest that homosexuality has a pattern of correlates largely, but not entirely, distinct from that identified among the paraphilias. At least, if homosexuality were deemed a paraphilia, it would be relatively unique among them, taxonometrically speaking.     

The Sex Ratio of Older Siblings in Non-Right-Handed Homosexual Men

This study tested the prediction, based on prior research, that non-right-handed homosexual men will report fewer than expected older brothers. Participants were 2486 heterosexual and homosexual, right-handed and non-right-handed, male and female adults, representing five samples collected for various projects by the second author. Data on sibship composition, sexual orientation, and hand-preference were gathered in the original research using on-line (Internet) or self-administered paper-and-pencil questionnaires. The non-right-handed homosexual men reported 83 older brothers per 100 older sisters, which was significantly lower than the human sex ratio of 106 live-born males per 100 live-born females. In contrast, the right-handed homosexual men reported 125 older brothers per 100 older sisters, which was significantly higher than the expected ratio. One possible explanation of these results is that older brothers increase the odds of homosexuality in right-handed males but decrease the odds of homosexuality in non-right-handed males. A second possibility is that older brothers decrease the probability that non-right-handed homosexual males will be represented in survey research. The latter scenario could arise if the combination of some biological factor associated with older brothers and some biological factor associated with non-right-handedness is so toxic that it kills the fetus or predisposes the individual to a condition (e.g., mental retardation, major mental illness) that makes him less likely to be available for research recruitment at Gay Pride parades (etc.) than other members of the gay community.     

Sexual orientation and eating psychopathology: the role of masculinity and femininity

OBJECTIVE: Previous research suggests that eating disorders are related to homosexuality in men, although links with female sexual orientation are less clear. Appearance factors have generally been implicated in this relationship. However, previous studies have failed to consider the role of femininity, even though evidence suggests that this is a more critical factor than sexual preference. The aim of this study was to consider the relationship between gender-role orientation and eating psychopathology in nonclinical men and women of different sexual orientations. METHOD: One hundred university students (40 homosexual; 60 heterosexual) completed the Bem Sex Role Inventory and the Eating Attitudes Test. RESULTS: For the group as a whole, there were links between femininity and high levels of eating psychopathology, whereas masculinity was associated with relatively healthy eating-related attitudes and behaviors. When considering the role of sexual orientation, these links were specific to homosexual men and women. CONCLUSIONS: In relation to homosexual men and women, the results support a model where femininity might be seen as a specific risk factor for eating disorders, whereas masculinity is likely to be a protective factor. Methodological and conceptual implications are discussed.     

Grade Failure and Special Education Placement in Sexual Offenders’ Educational Histories

A sample of 701 adult men underwent assessment following illegal or clinically significant sexual behaviors or interests. Patients were categorized on the basis of phallometric (penile) responses in the laboratory to erotic stimuli depicting adults, pubescent children, and prepubescent children; histories of sexual offenses; and self-reported sexual interests. Comprising the categories were men sexually interested in prepubescent children (pedophiles; n = 114), men sexually interested in pubescent children (hebephiles; n = 377), men sexually interested in adults and who had committed a sexual offense against an adult (teleiophilic offenders; n = 139), and men sexually interested in adults and who had no known history of any sexual offenses (teleiophilic nonoffenders; n = 71). Patients' assessments included IQ testing and self-reported academic history, which included any grade failures and assignment to special education classes. Relative to the teleiophilic offenders, both the pedophilic and the hebephilic groups showed approximately double the odds of failing a grade or being enrolled in special education, both before and after covarying IQ. No significant differences were detected between the teleiophilic offenders and the teleiophilic nonoffenders. These data are consistent with the hypothesis that an erotic age preference for children sometimes results from a perturbation of neurodevelopment occurring early in life.