Nature vs. Nurture

Scientists have yet to unlock the mysteries of sexual orientation, but significant research is underway. Learn about investigations into the biology of sexual orientation.

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Hi! I’m here to help you explore a fundamental question: What determines sexual orientation — nature or nurture? Scientists have learned the answer begins with an understanding of the two core elements involved: biological sex (the parts we’re born with) and attraction (who we’re drawn to, romantically and physically). In this section, we’ll investigate what else scientists have learned about the roots of sexual orientation. Let’s dig in…

Scientists explore same-sex attraction

Can genetics help explain the origins of same-sex attraction? What other factors are at play? Learn about a variety of scientific approaches and why researchers believe same-sex attraction is a natural variation in human evolution.

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National Geographic explores the science of same-sex attraction

Twin studies reveal important clues to the biology of same-sex attraction.

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“Diversity is nature’s secret weapon”

Same-sex attraction occurs throughout history in every culture and even in many animal species.

Controversies in science

Scientists face obstacles when it comes to researching the biology of sexual orientation.

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What’s at stake?

Learn about the challenges scientists face and why they are committed to their work.

Effects of social environments

Is it nature or nurture? These articles offer a peek into some of the research exploring the role of biology vs. society in shaping sexual identity.

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Can society make people gay?

Scientists dispute social hypotheses.

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A “near-perfect, quasi experiment”

A “near-perfect quasi-experiment” highlights the role of nature in shaping heterosexual attraction in men.

Our genes

Learn more about the role of genetics in shaping same-sex attraction.

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The search for a gay gene

Patterns of family member clustering influenced early efforts to identify a gay gene.

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Nature meets nurture in the field of epigenetics

Learn about epigenetics and how it relates to research on sexual orientation.

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Evolution partially explained

Learn about the research tracking how gay traits exist throughout family generations.

Hormones explored

Differences in hormone development have emerged as a key area of research on same-sex attraction for both men and women.

Thumbnail for Fraternal birth order linked to same-sex attraction in men

Fraternal birth order linked to same-sex attraction in men

Scientists have discovered that having older brothers increases the odds of a man being gay.

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The role of hormones explored

Scientists believe that hormonal differences may influence sexual orientation.

Thumbnail for Endocrine disorders linked to same-sex attraction in some women

Endocrine disorders linked to same-sex attraction in some women

Congenital adrenal hyperplasia (CAH) causes an overproduction of masculinizing hormones.

Glossary

Asexual

(Adj.) Describes a person who does not experience any form of sexual attraction. People who identify as asexual may or may not experience emotional, physical, or romantic attraction.

Bisexual

(Adj.) Refers to the sexual orientation of a person who experiences sexual, romantic, and/or emotional attraction to persons of more than one gender, not necessarily equally or at the same time, in the same way, or to the same degree. Also known as "bi".

Gay

(Adj.) Describes the sexual orientation of persons who are emotionally, sexually, and/or romantically attracted to persons of the same sex/gender. While the term is most often used to describe men, it can also be used more broadly to refer to both men and women (i.e., gay man, gay woman, gay people).

Heterosexual / Heterosexuality

(Adj.) Primary or exclusive sexual, emotional, and/or romantic attraction to a gender other than one's own. Typically this means a woman who is primarily attracted to men and vice versa. Also referred to as "straight".

Homosexual / Homosexuality

(Noun) A term that describes a primary or exclusive sexual, emotional, and/or romantic attraction to persons of one's own sex/gender. The term is considered outdated by many in the LGBTQ+ community but is still used in some research contexts.

Lesbian

(Adj./Noun) Refers to the sexual orientation of women who are emotionally, sexually, and/or romantically attracted to women.

Sexual orientation

(Noun) An enduring emotional, romantic, sexual or affectional attraction or non-attraction to other people. People use a variety of labels to describe their sexual orientation. Some of the better-known labels or categories include bisexual, pansexual, asexual, lesbian, gay or straight. Gender identity and sexual orientation are not the same. Transgender and gender non-conforming people may identify with any sexual orientation, and their sexual orientation may or may not change before, during or after gender transition.

Straight

(Adj.) Another term for heterosexual. Refers to the sexual, emotional, and/or romantic attraction to a gender other than one's own. Typically this means a woman who is primarily attracted to men and vice versa.

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Citations & Sources

Ashley, K. B. (2013). The Science on Sexual Orientation: A Review of the Recent Literature. Journal of Gay and Lesbian Mental Health, 17(2), 175-182. http://dx.doi.org/10.1080/19359705.2013.767179

Bailey, J.M., Vasey, P.L., Diamond, L.M., Breedlove, S.M., Vilan, E. & Epprecht, M. (2016). Sexual orientation, controversy, and science. Psychological Science in the Public Interest, 17(2), 45-101. doi:10.1177/1529100616637616

Blanchard, R. (2001). Fraternal birth order and the maternal immune hypothesis of male homosexuality. Hormones and Behavior, 40(2), 105-14. https://doi.org/10.1006/hbeh.2001.1681

Bogaert, A.F. (2006). Biological versus nonbiological older brothers and men's sexual orientation. Proceedings of the National Academy of Sciences of the United States of America, 103(28), 10771-4.

Burton, N. (2015, September 18). When Homosexuality stopped being a mental disorder. Retrieved from https://www.psychologytoday.com/blog/hide-and-seek/201509/when-homosexuality-stopped-being-mental-disorder

Cartwright, M. (2015, August 3). Where’s the scientific research into how sexual orientation develops in women? Slate. Retrieved from http://www.slate.com/blogs/outward/2015/08/03/sexual_orientation_in_women_why_so_little_scientific_r...

National Human Genome Research Institute (2016, April 1). Epigenomics. Retrieved from https://www.genome.gov/27532724/epigenomics-fact-sheet/

National Geographic. (2009, February 4). National Geographic explains the biology of homosexuality. Retrieved from https://www.youtube.com/watch?v=saO_RFWWVVA

Queen Mary, University of London. (2008, June 30). Homosexual behavior largely shaped by genetics and random environmental factors. Retrieved from www.sciencedaily.com/releases/2008/06/080628205430.htm

Reardon, S. (2015, October 8). Epigenetic 'tags' linked to homosexuality in men. Retrieved from http://www.nature.com/news/epigenetic-tags-linked-to-homosexuality-in-men-1.18530

Rice, W.R., Friberg, U., & Gavrilets, S. (2012). Homosexuality as a consequence of epigenetically canalized sexual development. The Quarterly Review of Biology, 87(4), 343-368. doi:10.1086/668167

Sanders, A.R., Martin, E.R., Beecham, G.W., Guo, S., Dawood, K., Rieger, G., Badner, J., Gershon, E.S., Krishnappa, R.S., Kolundzija, A.B., Duan, J., Gejman, P.J., & Bailey, J.M. (2015). Genome-wide scan demonstrates significant linkage for male sexual orientation. Psychological Medicine, 45(7), 1379-1388. doi:10.1007/s12119-014-9233-6

TEDx Talks. (2016, November 15). Homosexuality: It's about survival - not sex. Retrieved from https://www.youtube.com/watch?v=4Khn_z9FPmU&vl=en

Wolchover, N. (2012, June 11). Why are there gay men? Retrieved from https://www.livescience.com/33987-gay-men.html

Wolchover, N. (2012, June 12). Why are there gay women? Retrieved from https://www.livescience.com/33992-gay-women.html