Why are some people straight while others are gay or bisexual? What determines our sexual orientation anyway? Today, we’re going to be diving into what we’ve learned about the biological origins of our sexuality from decades of scientific research. As you’ll see, there’s not a simple and easy story—it doesn’t boil down to something like a “gay gene.” It’s way more complex than that!

I am joined once again by Nathan Lents, a Professor of Biology at John Jay College, where he is the director of the Cell and Molecular Biology program. His research lab studies human genetic evolution and forensic DNA technology. He also writes popular science articles and is the author of the new book The Sexual Evolution: How 500 Millions Years of Sex, Gender, and Mating Shape Modern Relationships.

Some of the specific topics we explore include:

Is same-sex attraction genetic?
How can two people who share 100% of the same DNA have different sexual orientations?
When researchers are studying sexual orientation, should they be looking at attraction, identity, behavior, or all of the above?
Why is having more older brothers linked to greater odds of homosexuality in men?
What other biological factors are associated with sexual orientation?

You can check out Nathan’s website to learn more about his work.

Got a sex question? Send me a podcast voicemail to have it answered on a future episode at speakpipe.com/sexandpsychology.

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Thank you to our sponsors!

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The Kinsey Institute at Indiana University has been a trusted source for scientific knowledge and research on critical issues in sexuality, gender, and reproduction for over 75 years. Be sure to register for the Sex and Aging Symposium , which will take place on October 4, 2025.

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Credits: Precision Podcasting (Podcast editing) and Shutterstock/Florian (Music). Image created with Canva; photos used with permission of guest.

Episode 425: What Determines Our Sexual ...