In Interesting Engineering, Trevor English surveys the common phenomenon of animals changing sex, and its physiological and genetic basis. For student-facing use, we recommend prefacing this article with a language distinction: Animals “change sex” meaning there is a change in their production of sex hormones and a physical change in their reproductive organs. Humans instead undergo “gender transition”, with “sex change” being an outdated term for this process.
Sex isn’t binary, and we should stop acting like it is
This article by Liza Brusman is available in English and Spanish, text or read loud.
Gynandromorph Animals - BBC Earth article
This BBC Earth article explores the rare phenomenon of bilateral gynandromorphs, or animals which develop different physical sex characteristics on their left and right side. This occurs when a cycle of meiosis yields multiple viable eggs rather than one egg and three polar bodies to be discarded. When two eggs are fertilized by sperm, mosaicism can occur in the sex chromosomes.
When introducing students to the article, the teacher should be sure to note that overgeneralizing language is briefly used to describe humans (“In humans, men have an X and a Y chromosome, while women have two X chromosomes.”) However, the article can still have value in demonstrating the nonbinary nature of biological sex and the scientific processes by which evidence is gathered to support this.
A Reddit post shows a gynandromorph lobster found in the wild:
Gender and Sex – Transgender and Intersex (Book Chapter)
This UMass Amherst textbook chapter models the use of precise, modern, and non-pathologizing language for discussing transgender and intersex topics in the context on human biology. The textbook authors are Miliann Kang, Donovan Lessard, Laura Heston, and Sonny Nordmarken. The chapter is available through Openbooks under a Creative Commons Attribution license.
Sex Determination – Why So Many Ways of Doing It?
Image shows simplified diagrams of some systems of sex determination - hermaphroditism in plants and fish, environmental sex determination in reptiles and plants, and genotypic sex determination in humans and birds.
This PLOS Biology article details the diverse mechanisms by which sex is determined in different species, how they evolved, and how they may look in the future. The article opens with a treatment of three common myths of sex determination.
Editor’s note: The term "hermaphrodite" is appropriate for referring to non-human animals with sex characteristics that do not fit typical binary notions of male or female bodies. For humans, “intersex” is the appropriate term—learn more here!
Although the entire reading is not for k-12 audiences, the three myths, Figure 3, Figure 4, and Box 2 are suitable for high school.
Journal: The Biological Contributions to Gender Identity and Gender Diversity: Bringing Data to the Table
This study is a review of evidence that gender identity is influenced by innate factors including genetics. The authors hypothesize that gender identity is a multifactorial complex trait with a heritable polygenic component, and that the study of this trait is important.
Although gender identity as a polygenic trait is only a hypothesis, this example could serve to show biology students how heritability studies can be used to gain a better understanding of a complex, socially relevant trait. Most textbooks cite skin color and height as examples of polygenic traits, and gender identity might be another to add to that list.
A Brief History of Twin Studies
Images shows twin brother astronauts Scott Kelly and Mark Kelly in front of a sliding glass door.
This article from Smithsonian Magazine summarizes how twin studies have been used untangle the influences of genes and the environment on particular traits. Twins have been used in the study of eugenics, I.Q., eating disorders, obesity, sexual orientation, and the effect of spaceflight on the body.
Resource: WHO Gender and Genetics
The World Health Organization website has a concise but comprehensive overview of the relationship between genetics, sex, and gender. This website presents an overview of the major ethical, legal, and social implications associated with gender and genetics. This website is a useful resource for students researching sex and gender in the context of genetics or health.