Sex differences in partner preferences in humans and animals

Abstract

One contribution of 16 to a theme issue 'Multifaceted origins of sex differences in the brain'. A large number of morphological, physiological and behavioural traits are differentially expressed by males and females in all vertebrates including humans. These sex differences, sometimes, reflect the different hormonal environment of the adults, but they often remain present after subjects of both sexes are placed in the same endocrine conditions following gonadectomy associated or not with hormonal replacement therapy. They are then the result of combined influences of organizational actions of sex steroids acting early during development, or genetic differences between the sexes, or epigenetic mechanisms differentially affecting males and females. Sexual partner preference is a sexually differentiated behavioural trait that is clearly controlled in animals by the same type of mechanisms. This is also probably true in humans, even if critical experiments that would be needed to obtain scientific proof of this assertion are often impossible for pragmatic or ethical reasons. Clinical, epidemiological and correlative studies provide, however, converging evidence strongly suggesting, if not demonstrating, that endocrine, genetic and epigenetic mechanisms acting during the pre-or perinatal life control human sexual orientation, i.e. homosexuality versus heterosexuality. Whether they interact with postnatal psychosexual influences remains, however, unclear at present.

The neural basis of sex differences in sexual behavior: A quantitative meta-analysis

“…This may account for the absence of any significant cortical role in rodent sexual arousal in either sex. In contrast, sexual preference is exclusively controlled by subcortical regions in both rodents and humans (Balthazart, 2016; Poeppl et al, 2016; Sakuma, 2008). …”

“…Such sex-specific hypothalamic autarchy may rest upon sex differences in the morphology and connectivity of this structure (Byne, 1998; Hines, 2010; Ibanez et al, 2001; Kilpatrick et al, 2006; Lenz and McCarthy, 2010; Makris et al, 2013; Pérez et al, 1990; Sá and Madeira, 2005; Wang et al, 2014). Furthermore, given its neuroanatomical specificity relating to sexual orientation and functional relevance for encoding sexual preferences (Balthazart, 2016; Bao and Swaab, 2011; LeVay, 2011; Poeppl et al, 2016), the sex differences in hypothalamus activation during sexual stimulation might well be represent the neural correlate of behavioral findings pointing to a less distinct sexual orientation in women (Bailey, 2009). …”

Multifaceted origins of sex differences in the brain

“…In this issue, Balthazart [33] reviews the existing literature on what is arguably the most robust behavioural sex difference in humans, sexual partner preference, and he directly relates this to findings in animals involving hormonal or genetic manipulation. Evidence that partner preference is a sexually differentiated trait is found in the impact of preventing oestradiol production in the developing male rodent brain, resulting in either no preference or a reversal towards preference for mounting males [34].…”

Birth order and recalled childhood gender nonconformity in Samoan men and fa'afafine

“…Exposure to hormones in utero, especially androgens, is widely hypothesized to impact the development of sexual orientation (see Balthazart, 2016;Bao & Swaab, 2011;Cohen-Bendahan, van de Beek, & Berenbaum, 2005;Ellis & Ames, 1987;Hines, Constantinescue, & Spencer, 2015). Additionally, the organizational effects of hormones have been implicated in the development of sex-typed behavior in childhood, as well other psychological traits such as empathy, physical aggression, mental-rotation abilities, and verbal fluency (for review see Hines et al, 2015).…”

“…The dual impact of hormonal and genetic factors is consistent with the view that certain sexstereotyped behaviour and cognitive patterns have a strong genetic basis, the effects of which are moderated by sex-differentiating hormones (e.g.,Balthazart, 2016; Ngun, Ghahramani, Sanchez, Bocklandt, & Vilain, 2011). The dual impact of hormonal and genetic factors is consistent with the view that certain sexstereotyped behaviour and cognitive patterns have a strong genetic basis, the effects of which are moderated by sex-differentiating hormones (e.g.,Balthazart, 2016; Ngun, Ghahramani, Sanchez, Bocklandt, & Vilain, 2011).…”