Oxytocin is sold in pop science as the cuddle hormone, but this episode argues it works more like a biological volume knob for tribalism. Its name comes from Greek words for swift birth. In 1906 British pharmacologist Henry Hallett Dale found that a pituitary extract made the uterus contract, and in 1953 American biochemist Vincent du Vigneaud sequenced and synthesized the nine amino acid hormone, winning the 1955 Nobel Prize in Chemistry. Made in the hypothalamus and released by the posterior pituitary, it drives labor through a rare positive feedback loop and triggers milk letdown, and evolution repurposed that pathway for bonding.

The evidence spans species: virgin sheep given oxytocin into cerebrospinal fluid mothered foreign lambs, knockout mice without receptors failed to recognize familiar mice, and wild chimpanzees showed higher urinary oxytocin after sharing food than after grooming. In humans, nasal spray studies raised trust in strangers. Then the darker turns: oxytocin promoted suspicion of outsiders, raised separation anxiety, and increased lying when the lie benefited a person’s group. A starfish relative, asterotocin, even made starfish evert their stomachs.

• Oxytocin spray making participants twice as likely to show the highest level of trust
• Partnered men keeping 10 to 15 centimeters more distance from an attractive stranger
• Testosterone inhibiting oxytocin release in mouse studies
• Why plasma oxytocin stays high, and anxiety rises, when couples are separated
• A blister study linking supportive conversation, higher oxytocin and faster wound healing