Family Size in White Gay and Heterosexual Men

Department of Mental Health Sciences, Royal Free and University College Medical School, London, United Kingdom.
Archives of Sexual Behavior (Impact Factor: 3.53). 03/2005; 34(1):117-22. DOI: 10.1007/s10508-005-1006-8
Source: PubMed


There is some evidence for a genetic influence on sexual orientation. However, gay men have fewer children than heterosexual men. Increased fecundity in the biological relatives of gay men could offset this selection pressure. We measured family size in gay (n = 301) and heterosexual (n = 404) men, attending clinics for sexually transmitted infections. The main outcome measure was the number of each man's uncles and aunts, first cousins, siblings, nephews and nieces, and his own children. With the exception of the participants' own offspring, mean family size of each category of relatives was significantly larger for gay men (paternal and maternal total OR = 1.02, CI = 1.01-1.03). This remained the case after adjustment for other predictors of family size (paternal and maternal total OR = 1.02, CI = 1.00-1.03). We found increased fecundity in the relatives of gay men and this is one explanation of how a genetic influence might persist in spite of reduced reproductive fitness in the gay phenotype. There are, however, a number of alternative explanations for our finding, including unknown psychological and social factors, which might mediate the association between family size and sexual orientation.

Download full-text


Available from: Michael B King, Dec 22, 2014
  • Source
    • "Cantor, Blanchard, Paterson, and Bogaert (2002) estimated that one in seven of gay men can attribute their sexual orientation to birth order. Moreover, several studies now report that other classes of siblings, such as sisters, can produce associations with birth order on male sexual orientation (Blanchard et al., 2002; Kangassalo, Pölkki, & Rantala, 2011; King et al., 2005). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The present study explored whether there were relationships between number of older brothers, handedness, recalled childhood gender nonconformity (CGN), and sexual orientation in men. We used data from previous British studies conducted in our laboratory (N = 1,011 heterosexual men and 921 gay men). These men had completed measures of demographic variables, number and sex of siblings, CGN, and the Edinburgh Handedness Inventory. The results did not replicate the fraternal birth order effect. However, gay men had fewer "other siblings" than heterosexual men (even after controlling for the stopping-rule and family size). In a sub-sample (425 gay men and 478 heterosexual men) with data available on both sibling sex composition and handedness scores, gay men were found to show a significantly greater likelihood of extreme right-handedness and non-right-handedness compared to heterosexual men. There were no significant effects of sibling sex composition in this sub-sample. In a further sub-sample (N = 487) with data available on sibling sex composition, handedness, and CGN, we found that men with feminine scores on CGN were more extremely right-handed and had fewer other-siblings compared to masculine scoring men. Mediation analysis revealed that handedness was associated with sexual orientation directly and also indirectly through the mediating factor of CGN. We were unable to replicate the fraternal birth order effect in our archived dataset but there was evidence for a relationship among handedness, sexual orientation, and CGN. These data help narrow down the number of possible neurodevelopmental pathways leading to variations in male sexual orientation.
    Archives of Sexual Behavior 02/2015; 44(5). DOI:10.1007/s10508-014-0474-0 · 3.53 Impact Factor
    • "1. OD, that is, heterozygous advantage in males. In this hypothesis (Hutchinson 1959; Weinrich 1987; MacIntyre and Estep 1993; King et al. 2005; Gavrilets and Rice 2006), a homozygous form would be maintained attributable to a selective advantage in the corresponding heterozygous form in males. As considered in CCZ, such OD mechanism does not coincide with the classical assumption in which heterozygous advantage is manifested in all carriers regardless of sex, because a tunable SA component is always present, the examined genetic factors being favorable to females. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Sexual conflict likely plays a crucial role in the origin and maintenance of homosexuality in our species. Although environmental factors are known to affect human homosexual (HS) preference, sibling concordances and population patterns related to HS indicate that genetic components are also influencing this trait in humans. We argue that multilocus, partially X-linked genetic factors undergoing sexually antagonistic selection that promote maternal female fecundity at the cost of occasional male offspring homosexuality are the best candidates capable of explaining the frequency, familial clustering, and pedigree asymmetries observed in HS male proband families. This establishes male HS as a paradigmatic example of sexual conflict in human biology. HS in females, on the other hand, is currently a more elusive phenomenon from both the empirical and theoretical standpoints because of its fluidity and marked environmental influence. Genetic and epigenetic mechanisms, the latter involving sexually antagonistic components, have been hypothesized for the propagation and maintenance of female HS in the population. However, further data are needed to truly clarify the evolutionary dynamics of this trait. Copyright © 2015 Cold Spring Harbor Laboratory Press; all rights reserved.
    Cold Spring Harbor perspectives in biology 01/2015; 7(4). DOI:10.1101/cshperspect.a017657 · 8.68 Impact Factor
    • "In a minority of studies, homosexual males showed preponderances of siblings in categories such as older sisters or younger siblings (Blanchard, 1997; Blanchard & Lippa, 2007; Kangassalo, Pölkki, & Rantala, 2011; King et al., 2005; VanderLaan & Vasey, 2011; Vasey & VanderLaan, 2007), but the finding regarding older brothers is by far the most robust and consistent finding across studies. Furthermore, when multiple sibling category effects exist, direct comparison of the magnitudes of these effects indicates that the older brother effect takes precedence (VanderLaan & Vasey, 2011). "
    [Show abstract] [Hide abstract]
    ABSTRACT: This study tested predictions regarding two hypothesized maternal immune responses influencing sexual orientation: one affecting homosexual males with high fraternal birth order and another affecting firstborn homosexual individuals whose mothers experience repeated miscarriage after the birth of the first child. Low birth weight was treated as a marker of possible exposure to a maternal immune response during gestation. Birth weight was examined relative to sibship characteristics in a clinical sample of youth (N = 1,722) classified as heterosexual or homosexual based on self-reported or probable sexual orientation. No female sexual orientation differences in birth weight were found. Homosexual, compared to heterosexual, males showed lower birth weight if they had one or more older brothers-and especially two or more older brothers-or if they were an only-child. These findings support the existence of two maternal immune responses influencing male sexual orientation and possibly also cross-gender behavior and identity. © 2014 Wiley Periodicals, Inc. Dev Psychobiol.
    Developmental Psychobiology 01/2015; 57(1). DOI:10.1002/dev.21254 · 3.31 Impact Factor
Show more