Testing Biological Theories of Same-Sex Sexual Attraction and Transgender Identity: Somatic, Cognitive, Behavioural, and Demographic Markers

性别认同和性取向是两种最大的心理性别差异。绝大多数人都是顺性别（即男性认为自己是男性，女性认为自己是女性），并表现出异性的吸引力。然而，这些基本模式也存在例外。大量少数人表现出同性性吸引和/或跨性别，因此为研究大脑、认知和行为的性别分化提供了独特的人类模型。******荷尔蒙、遗传和免疫过程已被假设影响大脑的性别分化，并导致性别认同和性取向的性别内变异。先前的研究考察了这些生物过程的躯体、认知、行为和人口统计学标记是否能够区分变性人和顺性人，以及同性和异性吸引的个体。与跨性别相关的生物标志物通常也与同性性吸引有关。然而，由于没有研究直接比较同性吸引的顺性人和变性人之间的这些生物标志物，因此尚不清楚这两种表型在多大程度上（如果有的话）是由不同的生物学过程支撑的。******为了澄清这个问题，我们必须考察一个人群，在这个人群中，比较同性吸引的顺性人和变性人是可行的。在西方国家，跨性别是罕见的，很难在专业诊所之外进行研究。因此，拟议的研究将在泰国进行，在那里，顺性别同性吸引相对普遍（2-5%），由于缺乏对性别表达的社会谴责，跨性别同性吸引比其他人群普遍50 - 250倍。因此，泰国人口提供了一个难得的机会来比较同性性取向和跨性别主义作为性别分化的人类模型。******泰国同性吸引的顺性人与变性人将在一套全面的相关生物标志物上进行比较。这些包括与产前雄激素暴露相关的几个标记：大脑结构（如皮质厚度、白质微观结构）、第二和第四指的比例、身体尺寸（如身高、体重）、面部结构、认知能力（如心理旋转）和行为特征（如用手习惯）。为了提供有关遗传和免疫因素的见解，将分别检查跨性别和同性性取向的熟悉程度以及参与者的出生顺序。******通过比较同性吸引的顺性人与变性人在一套全面的生物标志物上的差异，我的研究项目将改变我们对这些人类模型和生物标志物如何揭示大脑、认知和行为的性别分化的理解

Gender identity and sexual orientation are two of the largest psychological sex differences. The vast majority of people are cisgender (i.e., males identify as men, females identify as women) and exhibit opposite-sex attraction. Yet, exceptions to these fundamental patterns exist. Substantial minorities of people exhibit same-sex sexual attraction and/or transgenderism and, thus, provide unique human models for studying sexual differentiation of the brain, cognition, and behaviour.******Hormonal, genetic, and immunological processes have been hypothesized to influence sexual differentiation of the brain and lead to within-sex variation in gender identity and sexual orientation. Previous research examined whether somatic, cognitive, behavioural, and demographic markers of these biological processes differentiate transgender vs. cisgender individuals on the one hand, and same- vs. opposite-sex attracted individuals on the other. Biomarkers associated with transgenderism are often also associated with same-sex sexual attraction. Yet, because no studies directly compared these biomarkers across same-sex attracted cisgender vs. transgender individuals, it is unclear to what extent, if any, these two phenotypes are underpinned by different biological processes.******To clarify this issue, one must examine a population in which comparing groups of same-sex attracted cisgender vs. transgender individuals is feasible. In Western countries, transgenderism is rare and difficult to study outside of specialty clinics. Hence, the proposed research will be situated in Thailand where cisgender same-sex attraction is relatively common (2-5%) and, due to a lack of social censure regarding gender expression, transgender same-sex attraction is 50 to 250 times more common than in other populations. Thus, the Thai population provides a rare opportunity to compare same-sex sexual orientation and transgenderism as human models of sexual differentiation.******Thai same-sex attracted cisgender vs. transgender individuals will be compared on a comprehensive set of relevant biomarkers. These include several markers linked to prenatal androgen exposure: brain structure (e.g., cortical thickness, white matter microstructure), second-to-fourth digit ratio, physical size (e.g., height, weight), face structure, cognitive abilities (e.g., mental rotation), and behavioural characteristics (e.g., handedness). To provide insight regarding genetic and immunological factors, familiality of transgenderism and same-sex sexual orientation and participants' birth orders will be examined, respectively.******By comparing same-sex attracted cisgender vs. transgender individuals on a comprehensive set of biomarkers, my research program will transform our understanding of how these respective human models and biomarkers shed light on sexual differentiation of the brain, cognition, and behaviour.**