My interest in studying the biology of the diverse nature of human sexuality is a natural extension of my thirty-year effort to persuade the academic community to include biological sex as a variable in scientific research. Until the 1990’s, the “bikini-view” of women looked only at their reproductive function. We assumed that what we found out about the rest of human physiology from investigating men was also true of women without any direct evidence that this is the case –an absolutely unjustifiable intellectual error. Studying and comparing data from both sexes produced a global revolution in our thinking that produced what is now a robust and expanding science: gender specific medicine. It is the study of the differences in normal human physiology and in the experience of disease between men and women.

It wasn’t possible for me to consider differences between the sexes without an increasing consciousness of the importance of the fact that there were humans that did not fit neatly into the diadic, black and white division of male and female. Indeed, as a growing chorus of voices from the lay public points out, significant variations in sexual anatomy, sexual preference and even an awareness of sexual identity that is incongruent with genital anatomy exist.  It became clear that what we once thought we knew about biological sex, gender, and sexuality was outdated. The mapping of the human genome at the beginning of this century opened new avenues for thinking about how biological sex is established, maintained, and modified throughout a person’s lifetime. In fact, human biological sex, gender identity and preferences exist not in two separate, clearly defined buckets of male and female, but on a continuum in which each individual has a precise position.

Interestingly, my audiences in the scholarly environment of gender-specific medicine were not receptive to the notion that it was important to consider the biology of the entwined product of biological sex and the environment in forming sexual identify and function. I remember in particular one of the most accomplished scientists in gender-specific medicine telling me that homosexuality was a moral decision/aberration and that it was not a proper topic for serious investigation. In contrast, public attention to the nature and diversity of human sex/gender has been growing. More and more people are beginning to identify as part of an unexpectedly large, ever-expanding community. In a recent 2020 poll, Gallup found that 5.6% of American adults identifies as lesbian, gay, bisexual, or transgender (LGBT), up more than a percent from 2017—that is over four million more people in just four short years. Millennials are three times as likely than older generations to identify as LGBT; Gen Z, the largest and youngest generational group in the United States (as well as the world), are five times as likely. Indeed, it is now standard on applications for jobs, etc., to indicate a preferred personal pronoun: he/his; she/hers; they/their, etc.

The emergence of new concepts of the significant variability in human sexual identity and sexual preference has fostered a surge of social protests about the status and human rights of people who do not fit the conventional male/female categorization. “Conservatives” see minority groups as a threat to social health and order, but those minority groups are fighting back against the long-held status quo.

The increasing tolerance for variations in sexuality has not been universal: trans people, intersex people, and anyone who isn’t “straight” all face unique social consequences that range from subtle social isolation and outright shunning to murder. Just a month after the Pentagon signed a contract with the first transgender recruit into the U.S. military in February 2018, the Trump administration announced a new policy that banned most transgender people from service; these policies were once again reversed under the Biden administration by executive order in January 2021. The Equality Act, which has been introduced multiple times and has most recently been passed in the House of Representatives in 2021, is struggling for passage in the Senate; it would amend the 1964 Civil Rights Act to explicitly prevent discrimination based on sexual orientation and gender identity, which are not yet protected under federal law and is patchwork at state level. As of March 2021, approximately 29 state legislatures are debating bills that would ban trans girls and women from participating in sports that match their gender identities; this comes after the Biden administration’s Executive Order that said any school receiving federal funding must allow trans girls to participate in girls’ sports teams. The Arkansas state legislature passed a bill that would prohibit doctors from providing or even referring gender-affirming treatment to trans youth—against the recommendation of multiple medical best practice guidelines.

I published The Plasticity of Sex (9780128159682) for the scientific community with a particular focus on the variations in human sexuality, seeking to provide a comprehensive view of what we do—and do not—know about this important topic. Each of us has a fundamental biology that explains how we become who we are. Essentially, this book is an effort to direct specific attention to exploring the biological basis of human sexuality. It is also meant to detoxify the intense negativity of the public to the obvious variations that are more and more recognizable in the human family. Many new features of the biology of sex have emerged: for example, the role of the sex chromosomes, X and Y, turns out to be only part of the mechanism that defines sexual identify; Sarah Richardson’s work highlights  the myriad of genetic factors involved in the process and was an important factor in my own awareness of the complexity of the process. Eric Vilain’s and William Rice’s work on the possible role of epigenetics in shaping homosexuality are fundament contributions to our understanding of what shapes sexual preference. An impressive list of authorities contributed invaluable information to the book: Coolidge and Stillman write about the strong heritability of gender dysphoria, while the role of hormones on gender identity and gender role are explored in four other chapters. Ancillary and vitally important issues like the care of the transgender person, fertility preservation for transgender individuals, and the protection of the rights of intersex children are all included in the book. Techniques for incorporating new data about the analysis and documentation of sexual identity as well as the care of the populations that differ from the black/white categorization of biological sex are offered for inclusion in medical curricula.

Science, without much basis, has often been used inappropriately against the most vulnerable populations. This book seeks to detoxify the conversation surrounding the complex nature of human sexuality for the scientific community. Hopefully, it will correct the notion that variations in human sex, gender, and sexuality are best confined to a black and white, two bucket system with outliers defined as abberations to be suppressed, scorned and stripped of social and legal support.

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