Taxometric analyses of sexual orientation and gender identity.

Abstract

Taxa are nonarbitrary classes whose existence is an empirical question and not a matter of mere semantic convenience. Taxometric procedures detect whether numerical relations between purported indicators of conjectured taxa bear the hallmarks of true taxa. On the basis of theoretical considerations, the current study tested whether taxa underlie sexual orientation and related measures of gender identity. Two taxometric procedures, maximum covariance, making hits maximum (MAXCOV) and mean above minus below a cut (MAMBAC), were applied to Kinsey Scales and measures of childhood gender nonconformity and adult gender identity in a sample of nearly 5,000 members of the Australian Twin Registry. Results suggest that latent taxa underlie these measures. About 12-15% of men and 5-10% of women belong to latent taxa associated with homosexual preference. These percentages are greater than those of individuals who report homosexual preference, however, and hence it appears that an appreciable proportion of individuals in these taxa have heterosexual preference. An understanding of the origins of these latent taxa may be important to understanding the development of sexual orientation and gender identity.

Sexual Orientation and Psychiatric Vulnerability: A Twin Study of Neuroticism and Psychoticism

“…from exclusive attraction to the opposite sex (heterosexuality; Kinsey score 0), through degrees of attraction to both sexes (bisexuality; Kinsey scores 1-5), to exclusive attraction to the same sex (homosexuality; Kinsey score 6). Underlying this spectrum of sexual orientation, though, there appears to be a dichotomous factor with exclusive heterosexuals in one group and those with at least some homosexual tendencies in the other-a taxonometric analysis of our data suggested that up to 15% of men and 10% of women belong to the taxon associated with homosexuality (Gangestad, Bailey, & Martin, 2000). Note that we used sexual attraction as the indicator rather than sexual behavior or sexual identity, because we believe that attraction is less affected by mate availability and social/cultural constraints and is, in this sense, more fundamental (Sell et al, 1995).…”

Fraternal Birth Order and Extreme Right-Handedness as Predictors of Sexual Orientation and Gender Nonconformity in Men

“…Sexual orientation also appears mostly bimodal in its distribution and homosexuality is not simply the extreme end of a normal distribution of trait sexual orientation (even in females to an extent), another observation that works against a multifactorial model. This has led some to propose that only a very limitednumber ofdevelopmentalfactors could cause variations in sexual orientation although this explanation is also unsatisfying without proposing some theoretical tools for narrowing down putative factors (Gangestad, Bailey, & Martin, 2000;Rahman, 2005;Waddington, 1942). In contrast, the persistence Arch Sex Behav of modestly heritable sexual orientation, in the face of selection pressures against a trait that reduces reproductive fitness, argues against single factors (e.g., genes) of large effect.…”

Genetic and environmental influences on sexual orientation and its correlates in an Australian twin sample.

“…Multifactorial systems can generate nonnormal data due to either measurement biases (Grayson, 1987) or to nonlinear effects of genes and environments. The debate whether sexual orientation is dimensional or categorical (Gangestad, Bailey, & Martin, 1998;Haslam, 1997) is, for this reason, not especially germane to the validity of the multifactorial assumption. The multifactorial assumption can be falsified only by discovery of a gene or environment that is sufficiently large in effect to bias parameter estimates unduly.…”