LAUSR

Relyingprimarilyon indirectputative indicesof fetal testosterone (T) exposure (2D:4Ddigit ratios and otoacoustic emissions), Breedlove (2017) summarizes literature supporting the conclusionthat lesbianwomen,onaverage,areexposedtogreaterprenatal androgen than are straight women. By contrast, Breedlove argues that homosexual orientation inmen (based on these same putativeretrospectivemarkersof fetalandrogenaction)cannotbe easily explainedbya reduction inprenatal androgen. Instead, Breedlove suggests that there may be, as yet unidentified, brainspecific reductions in response to androgen in male fetuses who grow up to be gay. Breedlove argues persuasively that the nonhuman animal literature on the critical role of perinatal testosterone exposure in forming male-typical forebrain and/or spinal cord nuclear volume, neuronal number, and neuronal phenotype remainsthebedrockreasonforsuspectingthat theremustbesome link between fetal and/or early postnatal variations in circulating testosterone’s neural actions and adult sexual orientation in humans.He points out that in the few documented human examples of sex differences in brain and spinal cord neuronal morphology, thesizeof thesexdifferencesneverapproachthemagnitude of the homologous morphological sex differences seen in several rodent species aswell as ferrets andsheep.Breedlovealso alludestothelargeanimalliteratureonsexdifferencesinbehavior (usually without specifying types of behavior), saying: ‘‘Having spentmostofmyadult life investigatingsexdifferences inbehavior innon-humananimals,Ihavewonderedwhethertheresults of animal studies have any relevance to sex differences in human behavior.’’ In so far as the topic of Breedlove’s article concerns prenatal influences on human sexual orientation,wewere surprised that he barely mentions a sizable animal literature on the hormonal and neuralcontrolofmale-typical,aswellas female-typical, sexual partner preference. The single such animal study cited (Roselli, Larkin, Resko, Stellflug, & Stormshak, 2004) described the interesting correlative observation that a minority (*8% of the population screened) of male sheep (rams), when given a choice betweenmountinganestrouseweoranotherram,showedahomosexual preference and chose to mount the ram. The volume of a sexually dimorphic nucleus (ovine SDN) located at the border of themedial preoptic area/anterior hypothalamus (mPOA/AH)was significantly greater in heterosexual (gynephilic) rams than in ewes.Bycontrast, thevolumeof theSDNinandrophilic (homosexual) rams was significantly lower than in gynephilic rams, although its volumewas still significantly greater than the SDN of ewes. AsBreedlovepointsout, ithasbeendifficult toestablisheithera correlational or a causal linkage between observed sex dimorphisms in forebrain nuclear volume and the capacity of male and femaleanimals todisplaymatingoranyother typeofsocialbehavior. This is especially true if one restricts the analysis to themotor patternsassociatedwithmalecopulation.Thus, forexample,when given testosterone inadulthood,gonadectomized female, like male, rats display all of the features ofmale-typical copulation (mounts, intromission-like behaviors, ejaculation-like behaviors) in testswithanestrousfemale(Emery&Sachs,1975).Yet, there is a striking twofold–threefold difference (male greater than female) in the dimensions of theSDNnucleus in the rat POA/AH(Gorski, Gordon, Shryne,&Southam, 1978)—abrain region that has long been linked to the display of male copulation in numerous vertebrate species (Hull, Meisel, & Sachs, 2002). There is also disagreement in the literature (Arendash & Gorski, 1983; de Jonge & Michael J. Baum [email protected]