Dr. Melissa Ilardo on Huberman Lab: Why Behavior Alters DNA

While DNA sequence is largely fixed, gene expression is highly dynamic and influenced by environment and behavior on timescales from minutes to generations. Epigenetic changes—chemical tags on DNA and associated proteins—can arise from stressors like famine or trauma and be passed to descendants, as seen in Dutch famine survivors and refugee populations. These inherited epigenetic modifications may be adaptive in one context (e.g., food scarcity) but maladaptive in modern abundance.

Immersing the face in cold water while holding the breath triggers a reflex that slows heart rate, constricts peripheral vessels, and causes the spleen to contract, releasing ~10% more oxygen-rich red blood cells into circulation. This is a much larger acute oxygen boost than many popular training hacks provide. The effect is transient—once normal breathing resumes, the spleen gradually re-sequesters those cells—but in populations that dive constantly, this reflex becomes central to survival and performance.

Bajau sea nomads of Indonesia, who dive daily for food, have spleens about 50% larger than neighboring non-diving villagers living in similar environments. This difference is present in Bajau divers and non-divers alike, indicating a genetic rather than purely training effect. Genetic analyses identified a thyroid-related variant associated with higher-than-average thyroid hormone, larger spleens, and increased red blood cell counts—an erythropoietin-independent pathway that could one day inform legal performance enhancement or treatments for hypoxia.

Korean Haenyeo women on Jeju Island dive into very cold water, often into their 70s and 80s, and historically did so throughout pregnancy. Lifelong diving training produces an exaggerated dive reflex: some Haenyeo experience heart-rate drops of >40 beats per minute in under 15 seconds when submerging. Genetically, they also appear to carry variants that blunt diving-related blood pressure spikes, likely protecting against hypertensive pregnancy disorders such as preeclampsia—mechanisms that could be mined for future maternal-health therapies.

Both mice and humans tend to prefer mates whose major histocompatibility complex (MHC)—a key immune gene cluster—differs most from their own. In a classic study, people smelled sweaty T‑shirts of potential partners and rated most attractive the odors produced by individuals with the most dissimilar MHC. This ‘hybrid vigor’ bias increases immune gene diversity in offspring and shows how subconscious scent preferences can function as a sophisticated genetic filter.