Sexual orientation (homo- vs. heterosexuality) is one of many sex differences observed in humans. Sex differences can result from differential postnatal experiences (interaction with parents, environment) or from biological factors (hormones and genes) acting pre- or postnatally. The first option is often favored to explain sexual orientation although it is supported by little experimental evidence. In contrast, many sexually differentiated behaviors are organized during early life by an irreversible action of sex steroids. In particular, the preference for a male or female sex partner is largely determined in rodents by embryonic exposure to sex steroids. The early action of these steroids also seems to affect sexual orientation in humans. Indeed, clinical conditions associated with major endocrine changes during embryonic life often result in an increased incidence of homosexuality. Furthermore, multiple sexually differentiated behavioral, physiological, or even morphological traits that are known to be organized by prenatal steroids, at least in animals, are significantly different in homo- and heterosexual populations. Thus prenatal endocrine (or genetic) factors seem to influence significantly human sexual orientation even if a large fraction of the variance remains unexplained to date. The possible interaction between biological factors acting prenatally and postnatal social influences remains to be investigated.

Written with the same clarity, directness, and humor that have made Simon LeVay one of the most popular lecturers at Harvard Medical School and at the University of California, San Diego, The Sexual Brain examines the biological roots of human sexual behavior. It puts forward the compelling case that the diversity of human sexual feelings and behavior can best be understood in terms of the development, structure, and function of the brain circuits that produce them. Discarding all preconceptions about the motivation and purpose of sexuality, LeVay discusses the scientific evidence bearing on such questions as why we are sexual animals, what the brain mechanisms are that produce sexual behavior, how these mechanisms differ between men and women and how these differences develop, and finally, what determines a person's sexual orientation: genes, prenatal events, family environment, or early sexual experiences? The Sexual Brain is broad in scope, covering evolutionary theory, molecular genetics, endocrinology, brain structure and function, cognitive psychology, and development. It is unified by LeVay's thesis that human sexual behavior, in all its diversity, is rooted in biological mechanisms that can be explored by laboratory science. The book does not shy away from the complexities of the field, but it can be readily appreciated and enjoyed by anyone with an intelligent interest in sex.

What causes a child to grow up gay or straight? In this book, neuroscientist Simon LeVay summarizes a wealth of scientific evidence that points to one inescapable conclusion: Sexual orientation results primarily from an interaction between genes, sex hormones, and the cells of the developing body and brain. LeVay helped create this field in 1991 with a much-publicized study in Science, where he reported on a difference in the brain structure between gay and straight men. Since then, an entire scientific discipline has sprung up around the quest for a biological explanation of sexual orientation. In this book, LeVay provides a clear explanation of where the science stands today, taking the reader on a whirlwind tour of laboratories that specialize in genetics, endocrinology, neuroscience, cognitive psychology, evolutionary psychology, and family demographics. He describes, for instance, how researchers have manipulated the sex hormone levels of animals during development, causing them to mate preferentially with animals of their own gender. LeVay also reports on the prevalence of homosexual behavior among wild animals, ranging from Graylag geese to the Bonobo chimpanzee. Although many details remain unresolved, the general conclusion is quite clear: A person's sexual orientation arises in large part from biological processes that are already underway before birth. LeVay also makes it clear that these lines of research have a lot of potential because--far from seeking to discover "what went wrong" in the lives of gay people, attempting to develop "cures" for homosexuality, or returning to traditional explanations that center on parent-child relationships, various forms of "training," or early sexual experiences--our modern scientists are increasingly seeing sexual variety as something to be valued, celebrated, and welcomed into society.

Do biological factors, such as gonadal hormones, determine our sexual destiny after our genes are in place? Do they make men aggressive, or women nurturing? Do they cause boys and girls to play differently or to have different interests? Do they explain differences in sexual orientation within each sex group? Do they contribute to the preponderance of men in science or women at home? Scientists working from a psychosocial perspective would answer these questions differently than those working from a behavioral neuroscience or neuroendocrinological perspective. This book brings both of these perspectives to bear on the questions, tracing the factors that influence the brain, beginning with testosterone and other hormones during prenatal life, and continuing through changing life situations and experiences that can sculpt the brain and its activity, even in adulthood. This influence has important implications for understanding the social roles of men and women in society, the different educational and emotional issues that confront males and females, the legal rights of those whose sexual orientation or gender identity do not correspond to norms, and even standards of clinical care for people born with physical intersex conditions that make it difficult to classify a person as male or female at birth. This original and accessible book will be of interest to psychologists, neuroscientists, pediatricians, and educators, as well as the general public. It is also suitable for use in graduate and undergraduate courses on the psychology of gender or on hormones and behavior.

An official publication of the Alfred C. Kinsey Institute for Sex Research.

Female and male brains are different, thanks to hormones coursing through the brain before birth. That’s taught as fact in psychology textbooks, academic journals, and bestselling books. And these hardwired differences explain everything from sexual orientation to gender identity, to why there aren’t more women physicists or more stay-at-home dads. In this compelling book, Rebecca Jordan-Young takes on the evidence that sex differences are hardwired into the brain. Analyzing virtually all published research that supports the claims of “human brain organization theory,” Jordan-Young reveals how often these studies fail the standards of science. Even if careful researchers point out the limits of their own studies, other researchers and journalists can easily ignore them because brain organization theory just sounds so right. But if a series of methodological weaknesses, questionable assumptions, inconsistent definitions, and enormous gaps between ambiguous findings and grand conclusions have accumulated through the years, then science isn’t scientific at all. Elegantly written, this book argues passionately that the analysis of gender differences deserves far more rigorous, biologically sophisticated science. “The evidence for hormonal sex differentiation of the human brain better resembles a hodge-podge pile than a solid structure...Once we have cleared the rubble, we can begin to build newer, more scientific stories about human development.”

The increase in prevalence and visibility of sexually gender diverse (SGD) populations illuminates the need for greater understanding of the ways in which current laws, systems, and programs affect their well-being. Individuals who identify as lesbian, gay, bisexual, asexual, transgender, non-binary, queer, or intersex, as well as those who express same-sex or -gender attractions or behaviors, will have experiences across their life course that differ from those of cisgender and heterosexual individuals. Characteristics such as age, race and ethnicity, and geographic location intersect to play a distinct role in the challenges and opportunities SGD people face. Understanding the Well-Being of LGBTQI+ Populations reviews the available evidence and identifies future research needs related to the well-being of SDG populations across the life course. This report focuses on eight domains of well-being; the effects of various laws and the legal system on SGD populations; the effects of various public policies and structural stigma; community and civic engagement; families and social relationships; education, including school climate and level of attainment; economic experiences (e.g., employment, compensation, and housing); physical and mental health; and health care access and gender-affirming interventions. The recommendations of Understanding the Well-Being of LGBTQI+ Populations aim to identify opportunities to advance understanding of how individuals experience sexuality and gender and how sexual orientation, gender identity, and intersex status affect SGD people over the life course.