Scientific Understanding of Sexual Orientation: Implications for Science Education Ron Good Mark Hafner Patsye Peebles I N a recent issue of ABT, Chanley Small (1998) provides an updated view of the genetic determi- nants of sex, challenging us (and our students) to carefully consider the language we choose for defining sex or gender. In this paper we encourage readers to carefully consider the scientific basis of sexual orientation and to develop ways to present these ideas to students in life science courses. Recent books (cf. Burr 1996; Hamer & Copeland 1998; LeVay 1993; Pinker 1997) and articles (cf. Hamer et al. 1993; LeVay 1991; LeVay & Hamer 1994; and Pattatucci & Hamer 1995) make it clear that sexual orientation, like other traits, has a genetic basis. In fact, Alfred Kinsey’s much earlier work (Kinsey et al. 1948) was largely responsible for helping us begin to understand that the origins of sexual orientation, including homosexuality, are genetically influenced. Handedness & Sexual Orientation This heading does not refer to a correlation between handedness and sexual orientation. Following Burr (1996), handedness is used here as an analogy to discuss sexual orientation. Many of the statistics in this section can be found in his book A Separate Creation: The Search for the Biological Origins of Sexual Orientation. In past generations the expression of left-handed- ness (particularly handwriting) in infants and young children was often suppressed by parents, teachers and others who believed it was somehow unnatural (‘‘left hand’’ in Latin  sinister). Since the vast majority of people are right-handed, it was easy for the majority to believe they were right (so to speak) and left-handers would simply have to change their Ron Good is Professor of Science Education in the Depart- ment of Curriculum & Instruction at Louisiana State University, Baton Rouge, LA 70803; e-mail: rgood@lsu.edu. Mark Hafner is Professor of Biology in the Department of Biological Sci- ence and Director of the Natural Science Museum at Louisi- ana State University; e-mail: namark@lsu.edu. Patsye Pee- bles is Instructor of Biology in the Science Department at the Louisiana State University Laboratory School; email: ulpeeb@unix1.sncc.lsu.edu. 326 THE AMERICAN BIOLOGY TEACHER, VOLUME 62, NO. 5, MAY 2000 behavior. Now, at least in this country, we understand that handedness is not a choice, in the normal sense of that term, and we no longer try to suppress left-handers from expressing this trait (Burr 1996; Kalat 1998). Like handedness, society can suppress the behavior associated with sexual orientation (homosexuality in this case), but we cannot change its biological basis (Hamer & Copeland 1994; Kalat 1998). For both handedness and sexual orientation (heterosexual and homosexual), the trait appears at about 2 years of age and, unless suppressed by outside factors (par- ents, peers, clergy, teachers, etc.), will be expressed as the child grows older (Burr 1996; Hamer & Copeland 1994). For handedness, monozygotic twins are 1.5 times more likely than dizygotic twins to share the trait, but for sexual orientation monozygotic twins are 10 times more likely to share the trait (Burr 1996). For handedness, the minority orientation (lefties) is about 8% and for sexual orientation it is about 5% (although some estimates are as high as 10%) of the total population (Burr 1996). The minority orientation in both handedness and sexual orientation does not seem to correlate with race or culture but it does correlate with gender (Burr 1996; Hamer & Copeland 1994). For handedness, the minority orientation is about 30% higher in men than women, and for sexual orientation the minority orientation is about 50% higher in men than women (Burr 1996). Many studies from a wide variety of sources support these findings (Bailey & Pillard 1991; Bailey et al. 1993; Burr 1996; Gonsiorek & Weinrich 1991; Kinsey et al. 1948) so that at this time the scientific community no longer seriously questions their conclusions. For both hand- edness and sexual orientation, this kind of demographic research is essentially complete. The interesting ques- tion now for many scientists is, What mechanisms are involved? What is the genetic/biological basis of these orientations and what are the corresponding implications for nature-nurture controversies? Genetic Origins of Sexual Orientation On August 30, 1991, an article by Salk Institute neuroscientist Simon LeVay appeared in the journal