Behaviors That Alter Your Genes to Improve Your Health & Performance | Dr. Melissa Ilardo

Summary

Dr. Melissa Ilardo, professor of biomedical informatics at the University of Utah, discusses the intersection of human genetics, epigenetics, and how behavior shapes gene expression — both within a lifetime and across generations. The conversation explores real-world examples of natural selection in living human populations, including breath-hold diving communities whose physiology has genetically adapted to underwater life. Key topics include the mammalian dive reflex, spleen function, mate selection via immune system smell, and the inheritance of trauma-related epigenetic changes.

---

Key Takeaways

• Epigenetic changes can be inherited: Stress, famine, and trauma can leave molecular modifications on the genome that are passed to subsequent generations — sometimes as adaptive advantages, sometimes as liabilities in changed environments.
• The mammalian dive reflex triggers a 10% oxygen boost: Holding your breath while submerging your face in cold water (~10°C / 50°F) causes the spleen to contract and release stored red blood cells into circulation — a significant, measurable performance effect.
• Spleen size correlates with diving ability: The Bajau sea nomads of Indonesia have spleens approximately 50% larger than nearby non-diving populations, partly due to a genetic variant linked to higher-than-average thyroid hormone levels.
• Humans select mates based on immune system compatibility: People are subconsciously attracted to the body odor of individuals with the most different major histocompatibility complex (MHC), optimizing immune diversity in offspring.
• Human evolution is ongoing: Globalization is producing genetic combinations never before seen in human history, creating both new resilience and novel disease risks.
• Breath-hold training slows heart rate dramatically: Korean Haenyeo divers show heart rate drops of 40+ beats per minute in under 15 seconds — a trainable adaptation through a lifetime of diving.
• Diving through pregnancy has driven genetic blood pressure adaptations: The Haenyeo appear to carry a variant that lowers diastolic blood pressure during breath-holds, potentially protecting against hypertensive disorders of pregnancy.
• Evolution is not directional: “Survival of the fittest” is better understood as “best fit for the current environment” — evolution has no endpoint or goal.
• Inbreeding concentrates harmful recessive variants: Mating between closely related individuals dramatically increases the chance that deleterious genetic variants will be expressed in offspring.

---

Detailed Notes

Epigenetics and Behavioral Gene Expression

• Epigenetics involves molecules physically attaching to the genome and modifying how genes are expressed — without changing the underlying DNA sequence.
• These modifications can be passed to subsequent generations.
• Example: Dutch famine survivors passed epigenetic changes to their children. These changes likely helped descendants survive food scarcity but may be disadvantageous in modern environments of food abundance.
• Trauma in refugee populations has also been recorded in heritable epigenetic changes, though whether these are adaptive or maladaptive is not fully understood.
• Gene expression changes can occur on the timescale of minutes to hours (environmental response) or across generations (epigenetic inheritance).

Natural Selection Timelines

• Classical assumption: meaningful genetic selection requires 5,000–10,000+ years.
• Updated understanding: selection can occur in as little as 1,000–2,000 years under strong environmental pressure.
• Most mutations are deleterious — many are filtered out before birth.
• Beneficial adaptations most often come from standing variation: existing genetic diversity in a population that becomes advantageous under new conditions.

Mate Selection and the Immune System

• Studies replicating mouse MHC research in humans confirmed: people are more attracted to the body odor of individuals with maximally different immune system profiles.
• Participants smelled sweaty t-shirts from opposite-sex individuals; attraction correlated with MHC dissimilarity.
• This suggests smell functions as a proxy for offspring immune diversity, operating below conscious decision-making.
• The opposite pattern — inbreeding — dramatically increases expression of harmful recessive variants and has been culturally discouraged across human societies long before genetics was understood.

Hybrid Vigor and Globalization

• Globalization is creating genetic combinations that have never existed in human history, potentially increasing population-level resilience.
• Historical example: The Tibetan high-altitude adaptation was likely acquired through interbreeding with Denisovans (archaic hominids), providing genes enabling survival at extreme elevations.
• Similar introgression (gene transfer between species/populations) occurred with Neanderthals.
• New genetic combinations can also produce novel disease risks when variants that evolved separately are combined for the first time.

The Bajau Sea Nomads and the Mammalian Dive Reflex

• The Bajau people of Indonesia are sea nomads who have practiced breath-hold diving for generations. Children learn to swim before they walk.
• Reported breath holds: anecdotally up to 13 minutes (active diving, not static floating).
• The mammalian dive reflex is triggered by:
  • Breath-holding
  • Cold water on the face (stimulates the vagus nerve)
  • Protocol: face submerged in ~10°C / 50°F water
• Physiological responses:
  • Heart rate slows (peripheral vasoconstriction)
  • Blood vessels in extremities constrict (centralizes blood flow to brain and organs)
  • Spleen contracts, releasing stored oxygen-rich red blood cells into circulation
• The oxygen boost from spleen contraction: approximately 10%
• The spleen refills with red blood cells after the breath hold ends — the boost is transient and only active during the dive.
• The spleen also contracts during exercise, which may explain the disproportionately large spleens in horses and greyhounds.

Spleen Size, Genetics, and Thyroid Hormone

• Bajau divers and non-divers from the same community both have spleens ~50% larger than nearby farming populations — indicating a genetic, not purely training-based difference.
• The associated genetic variant correlates with higher-than-average (but not clinically elevated) thyroid hormone levels.
• This variant is also found in European populations, where it similarly predicts larger spleen size.
• Proposed mechanism: higher thyroid hormone → increased red blood cell production → larger spleen → more oxygen available during dives.
• Also results in increased hemoglobin, hematocrit, and red blood cell count.
• Importantly, this appears to be an erythropoietin (EPO)-independent mechanism of red blood cell increase — potentially relevant to performance enhancement research.
• Whether regular breath-hold training increases spleen size in non-Bajau individuals remains an open question; some training studies suggest it does.

The Haenyeo: Korean Female Divers

• The Haenyeo (“sea women”) of Jeju Island, South Korea, are an all-female diving community with an average age of approximately 70 years.
• They dive in extremely cold water, historically without wetsuits (cotton swimsuits until the 1980s).
• They dive throughout pregnancy, sometimes until the day of birth, returning to the water days postpartum.
• An 81-year-old diver participated in recent research; divers tracked diving to depths of approximately 10 meters (30 feet).
• They are a UNESCO Intangible Cultural Heritage.

Two Adaptations Found in the Haenyeo:

1. Trained Adaptation — Heart Rate Response

• Haenyeo divers show heart rate drops of 40+ beats per minute in under 15 seconds upon submersion.
• This is only present in divers, not in non-diving women from the same population → confirms it’s a training adaptation, not genetic.
• Suggests the heart develops significant autonomic plasticity through decades of diving practice.

2. Genetic Adaptation — Blood Pressure Regulation

• Diving through pregnancy mimics the oxygen deprivation of sleep apnea, which increases risk for preeclampsia and other hypertensive disorders of pregnancy.
• The Haenyeo carry a genetic variant associated with lowered diastolic blood pressure during breath-holds.
• This is believed to be a protective adaptation selected over generations of pregnant women diving.
• Researchers hope this