Why Don’t You Have Sex With Your Sister? - Dr Debra Lieberman

Dr. Debra Lieberman is an evolutionary psychologist, professor, and researcher. Why don’t we feel sexual attraction toward our siblings or close family? Evolution seems to have hard-wired the brain to prevent inbreeding, a pattern shared with many other animals. So how does this mechanism work, and what are the moral or ethical arguments surrounding incest? Expect to learn why evolution has designed you to not want to have sex with your sister, how animals actually detect who their relatives are, what the high level explanation is for why humans don’t want to have sex with their kin, the moral argument if it is okay for two adult siblings had consensual sex, how big the actual genetic risk is for first cousins, what crying and tears actually communicate from an evolutionary perspective and much more… Follow her work here: https://deblieberman.com/ - 0:00 Why Don’t We Want to Have Sex With Our Siblings? 7:57 What Cues Trigger Our Incest Avoidance Mechanism? 19:04 Is Incest Disgust a Moral Pressure? 27:19 How Only Children Make Sense of Incest 31:11 Why Is Incest P**n So Popular? 37:19 Why Do We Cry? 52:53 What Happens When No One is Watching 58:07 Why We Use Tears to Convey Emotions 01:06:30 Where to Find Debra - New pricing since recording: Function is now just $365, plus get $25 off at https://functionhealth.com/modernwisdom Get 35% off your first subscription on the best supplements from Momentous at https://livemomentous.com/modernwisdom Get a free bottle of D3K2, an AG1 Welcome Kit, and more when you first subscribe at https://ag1.info/modernwisdom Get a Free Sample Pack of LMNT’s most popular flavours with your first purchase at https://drinklmnt.com/modernwisdom - Get access to every episode 10 hours before YouTube by subscribing for free on Spotify - https://spoti.fi/2LSimPn or Apple Podcasts - https://apple.co/2MNqIgw Get my free Reading List of 100 life-changing books here - https://chriswillx.com/books/ Try my productivity energy drink Neutonic here - https://neutonic.com/modernwisdom - Get in touch in the comments below or head to... Instagram: https://www.instagram.com/chriswillx Twitter: https://www.twitter.com/chriswillx Email: https://chriswillx.com/contact/

Chris WilliamsonhostDr. Debra Liebermanguest

Jan 3, 20261h 8mWatch on YouTube ↗

EPISODE INFO

Released: January 3, 2026
Duration: 1h 8m
Channel: Modern Wisdom
Watch on YouTube: ▶ Open ↗

EPISODE DESCRIPTION

Dr. Debra Lieberman is an evolutionary psychologist, professor, and researcher. Why don’t we feel sexual attraction toward our siblings or close family? Evolution seems to have hard-wired the brain to prevent inbreeding, a pattern shared with many other animals. So how does this mechanism work, and what are the moral or ethical arguments surrounding incest? Expect to learn why evolution has designed you to not want to have sex with your sister, how animals actually detect who their relatives are, what the high level explanation is for why humans don’t want to have sex with their kin, the moral argument if it is okay for two adult siblings had consensual sex, how big the actual genetic risk is for first cousins, what crying and tears actually communicate from an evolutionary perspective and much more… Follow her work here: https://deblieberman.com/ - 0:00 Why Don’t We Want to Have Sex With Our Siblings? 7:57 What Cues Trigger Our Incest Avoidance Mechanism? 19:04 Is Incest Disgust a Moral Pressure? 27:19 How Only Children Make Sense of Incest 31:11 Why Is Incest P**n So Popular? 37:19 Why Do We Cry? 52:53 What Happens When No One is Watching 58:07 Why We Use Tears to Convey Emotions 01:06:30 Where to Find Debra - New pricing since recording: Function is now just $365, plus get $25 off at https://functionhealth.com/modernwisdom Get 35% off your first subscription on the best supplements from Momentous at https://livemomentous.com/modernwisdom Get a free bottle of D3K2, an AG1 Welcome Kit, and more when you first subscribe at https://ag1.info/modernwisdom Get a Free Sample Pack of LMNT’s most popular flavours with your first purchase at https://drinklmnt.com/modernwisdom - Get access to every episode 10 hours before YouTube by subscribing for free on Spotify - https://spoti.fi/2LSimPn or Apple Podcasts - https://apple.co/2MNqIgw Get my free Reading List of 100 life-changing books here - https://chriswillx.com/books/ Try my productivity energy drink Neutonic here - https://neutonic.com/modernwisdom - Get in touch in the comments below or head to... Instagram: https://www.instagram.com/chriswillx Twitter: https://www.twitter.com/chriswillx Email: https://chriswillx.com/contact/

SPEAKERS

Chris Williamson
host
Dr. Debra Lieberman
guest

EPISODE SUMMARY

In this episode of Modern Wisdom, featuring Chris Williamson and Dr. Debra Lieberman, Why Don’t You Have Sex With Your Sister? - Dr Debra Lieberman explores how Evolution Shapes Incest Taboos, Attraction, Disgust And Tears Dr. Debra Lieberman explains how humans evolved specialized psychological mechanisms to detect genetic relatives and avoid inbreeding, using cues like shared childhood co-residence and maternal caregiving. The same "kin detection" system that inhibits sexual attraction to close family also supports altruism toward them, and its imperfections show up in edge cases like sperm-donor siblings and cousin relationships. She and Chris Williamson then explore why incest taboos feel so viscerally strong, why some people lack that gut-level disgust, and why incest-themed porn or cousin attraction can still exist despite strong biological constraints. In the second half, Lieberman outlines a new evolutionary theory of crying as a social signal used by lower-leverage individuals to broadcast vulnerability, negotiate treatment, and mark what they value, across sadness, joy, pain, and grief.

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