How Hormones Shape Sexual Orientation & Behavior | Dr. Marc Breedlove

Andrew Huberman

Mar 30, 2026

Episode description

Dr. Marc Breedlove, PhD, is a professor of neuroscience at Michigan State University and an expert on how hormones shape brain development and sexual orientation. We discuss how prenatal testosterone impacts whether someone is romantically attracted to men or women later in life, and what correlates of sexual orientation — such as finger-length ratios — tell us about the role of hormones in brain and psychological development. We also discuss why the number of older brothers a male has biases sexual orientation. Throughout, we explain how nature and nurture interact to shape male-female differences, behavior, and romantic partner choice.

Show notes: https://go.hubermanlab.com/iJe27oR

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Dr. Marc Breedlove
Website: https://marcbreedlove.com
Curriculum vitae: https://docs.google.com/document/d/1mj4jJNGNUTtmiGkY9gMxRftfr4MovUD959Qi1Y-3z8Y/edit?tab=t.0
Books: https://marcbreedlove.com/books
Publications: https://pubmed.ncbi.nlm.nih.gov/?term=breedlove+sm&sort=date
TED talk: https://www.youtube.com/watch?v=3HX-A89XI3I
Whom You Love lectures: https://www.youtube.com/user/WhomYouLove2012
YouTube: https://www.youtube.com/@Dr.Breedlove/playlists
LinkedIn: https://www.linkedin.com/in/marcbreedlove

Timestamps
00:00:00 Marc Breedlove
00:03:24 Hormones & Sexual Orientation
00:07:37 Prenatal Testosterone, Finger Ratio, Men & Women Differences
00:14:08 Sponsors: David & Rorra
00:16:46 Finger Ratios, Prenatal Testosterone, Gay & Straight Men/Women
00:23:57 Mice & Sex Differences, Androgens
00:26:54 Brain Differences & Sexual Orientation
00:33:52 Group vs Individual Differences, Height Analogy; Bisexuality
00:36:57 Brain Development, Hormones & Behavior; Brain Plasticity
00:42:52 Sponsor: AG1
00:44:16 Sexual Behavior, Libido
00:51:37 Gay Rams, Brain Differences
00:58:00 Aversion Pathway, Men vs Women, Same-Sex Partner
01:06:58 Congenital Adrenal Hyperplasia (CAH), Intersex Phenotypes
01:13:55 Androgen Insensitivity Syndrome (AIS)
01:18:14 Sponsor: Function
01:19:25 Gay Men & Older Brothers, Maternal Immunization Hypothesis
01:32:55 CAH Carriers, Advantage, Stress Tolerance
01:35:41 Birds & Sexual Differentiation, Gynandromorphs
01:41:32 Anabolic Steroids, Hypersexuality; Adult Brain Plasticity
01:45:31 Age & Testosterone Decline; Sexual Orientation & Activities
01:53:14 Marc’s Academic Journey, Ozarks, Luck
02:02:35 Exploration; Kids & Sex Differences
02:08:47 Zero-Cost Support, YouTube, Spotify & Apple Follow, Reviews & Feedback, Sponsors, Protocols Book, Social Media, Neural Network Newsletter

#HubermanLab #Science #Hormones

Disclaimer & Disclosures: https://www.hubermanlab.com/disclaimer

Mindsip insights from this episode:

Recognize brain's expanding plasticity for continuous growth

A long-time neuroscience researcher observed that every year at scientific meetings, the brain is shown to be more plastic than the year before, indicating our understanding of its capacity for change is constantly expanding.

#neuroplasticity

Analyze finger length to understand prenatal hormone exposure

The ratio of the index finger to the ring finger (2D:4D) is a physical marker of prenatal testosterone exposure, as the fourth digit has more androgen receptors and grows longer in response to testosterone.

#testosterone

Understand masculine sexual attitudes in gay men

In terms of sexual attitudes like interest in multiple partners and casual sex, gay men are typically masculine, suggesting the key difference from straight men is not the amount of prenatal testosterone but how their brains responded to it.

#gender

Acknowledge maternal immune response to influence subsequent sons' development

A mother's body can 'remember' previous sons via an immune response that may alter the brain development of subsequent sons, increasing their probability of being gay.

#genetics

#immune-system

Recognize prolonged fetal growth in brain development until age six

The human brain continues its rapid fetal rate of growth until at least age six, meaning children are effectively fetuses learning and developing outside the womb.

#brain

#children

Understand attraction and aversion circuits in sexual preference

Sexual preference is not just about attraction to one sex, but may also involve a distinct biological circuit that creates an aversion to the other, a phenomenon observed in gay rams that will never mount a female.

#neurology

Embrace sexual fluidity to understand women's orientation dynamics

Women are generally more plastic in their sexual orientation throughout life than men, possibly because they lack the strong biological 'aversive' signal against same-sex partners that some men may have.