The Scientific American web-site has the above article, dated April 25, 2017. Its entitled, "Cross-Cultural Evidence for the Genetics of Homosexuality - Mexico's third gender sheds light on the biological correlates of sexual orientation."
Here's the link to the article: https://www.scientificamerican.com/article/cross-cultural-evidence-for-the-genetics-of-homosexuality/?wt.mc=SA_Facebook-Share
And the first few paragraphs ...
The reasons behind why people are gay, straight, or bisexual have long been a source of public fascination. Indeed, research on the topic of sexual orientation offers a powerful window into understanding human sexuality. The Archives of Sexual Behavior recently published a special edition devoted to research in this area, titled “The Puzzle of Sexual Orientation.” One study, conducted by scientists at the University of Lethbridge in Alberta, Canada, offers compelling, cross-cultural evidence that common genetic factors underlie same-sex, sexual preference in men.
In southern Mexico, individuals who are biologically male and sexually attracted to men are known as muxes. They are recognized as a third gender: Muxe nguiiu tend to be masculine in their appearance and behavior, while muxe gunaa are feminine. In Western cultures, they would be considered gay men and transgender women, respectively.
Several correlates of male androphilia — biological males who are sexually attracted to men — have been shown across different cultures, which is suggestive of a common biological foundation among them. For example, the fraternal birth order effect—the phenomenon whereby male androphilia is predicted by having a higher number of biological older brothers—is evident in both Western and Samoan cultures.