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

Here are the top 10 key takeaways from Dr. Melissa Elardo's discussion with Andrew Huberman about human genetics, evolution, and the remarkable adaptations found in diving populations around the world.

1. Blue eyes trace back to a single ancestor

All people with blue eyes descend from one individual who first developed this trait through genetic mutation. This remarkable fact illustrates how a single genetic change can spread throughout human populations over thousands of years. The mutation likely became widespread because blue eyes were considered an attractive and interesting feature, leading to increased reproductive success for those carrying the variant.

Green eyes, in contrast, arose from multiple genetic events across different populations. This demonstrates how similar traits can evolve independently through different genetic pathways. Brown eyes represent the original human eye color, making blue and green eyes relatively recent evolutionary developments in human history.

2. Humans possess an innate mammalian dive reflex

When you hold your breath and put your face in cold water, your body automatically triggers the mammalian dive reflex. This response includes heart rate reduction, blood vessel constriction in extremities, and most remarkably, spleen contraction. The spleen acts as a biological reservoir for oxygen-rich red blood cells, releasing them into circulation during the dive response.

This reflex provides approximately 10% more oxygen availability during breath holding. The response exists in all mammals, including mice that can be trained to dive. While humans aren't naturally aquatic, this ancient evolutionary mechanism suggests our distant ancestors may have engaged in diving behaviors, or it represents a preserved trait from early mammalian evolution.

3. Indonesian sea nomads evolved enlarged spleens for diving

The Bajo people of Indonesia, known as sea nomads, have spleens that are 50% larger than non-diving populations. These remarkable individuals can hold their breath for up to 13 minutes while actively hunting underwater at depths where they collect black coral, which only grows at 100 feet or deeper. Their children often learn to swim before walking, and some adults have feet so soft from minimal land contact that walking becomes difficult.

This enlarged spleen trait appears in both divers and non-divers within the population, indicating genetic rather than training-based adaptation. The larger spleen provides a greater reservoir of oxygen-carrying red blood cells, essentially functioning as a biological scuba tank. This adaptation likely evolved because poor diving ability meant death in the open ocean, removing individuals from the gene pool while successful divers survived to reproduce.

4. Korean female divers demonstrate extreme cold water adaptation

The Haenyeo of South Korea are an all-female diving population with an average age of 70 years old. Until the 1980s, they dove in freezing waters wearing only cotton bodysuits with no thermal protection. These women continue diving throughout pregnancy, sometimes until the day of birth, and return to the water within days postpartum. Many don't retire until they're over 100 years old.

Their extreme diving practices have shaped unique evolutionary adaptations. The population shows genetic variants that help lower blood pressure during diving, potentially protecting against hypertensive disorders that typically affect pregnant women experiencing sleep apnea. Their heart rates can drop more than 40 beats per minute in under 15 seconds during dives, representing an extraordinary training adaptation that may contribute to their remarkable longevity and fitness into advanced age.

5. Thyroid hormone levels influence spleen size and diving ability

Research revealed that successful diving populations carry genetic variants associated with higher-than-average thyroid hormone levels. These elevated levels correlate with increased red blood cell production, larger spleen size, and enhanced oxygen-carrying capacity. The connection isn't limited to diving populations - Europeans carrying the same genetic variants also show larger spleens and higher thyroid hormone levels.

This mechanism appears to work independently of EPO (erythropoietin), the hormone famously used by cyclists for performance enhancement. The thyroid-mediated pathway represents a natural method for increasing red blood cell count and oxygen availability. This discovery has potential implications for treating hypoxia-related conditions and understanding how behavioral demands can drive rapid evolutionary changes in human populations.

6. Genetic selection can occur within 1,000-2,000 years

Contrary to previous beliefs that human evolution requires 5,000-10,000 years, Dr. Elardo's research demonstrates that significant genetic changes can occur within 1,000-2,000 years. This accelerated timeline becomes possible when environmental pressures are severe enough to affect survival and reproduction. Diving populations face life-or-death consequences daily, creating intense selective pressure that rapidly favors beneficial genetic variants.

The Tibetan high-altitude adaptation provides another example of rapid human evolution. This trait, which helps people survive at extreme elevations, actually originated from genetic material acquired through interbreeding with Denisovans, an archaic human species. The genes remained dormant until Tibetan ancestors moved to high altitudes, where they suddenly became advantageous and spread rapidly through the population.

7. Mate selection unconsciously favors genetic diversity

Humans instinctively choose partners with immune systems most different from their own, as demonstrated through sweaty t-shirt experiments. When people smell clothing worn by potential partners, they consistently rate as most attractive those individuals whose major histocompatibility complex differs most from their own. This unconscious selection mechanism promotes genetic diversity in offspring, providing children with broader immune system protection against various pathogens.

This pattern mirrors behavior observed in mice and reflects an ancient biological drive toward hybrid vigor. With increasing globalization, humans are creating genetic combinations never before possible in human history. These novel genetic pairings may produce both enhanced resilience and new disease susceptibilities as previously separated genetic variants combine in single individuals.

8. Environmental behavior can modify gene expression across generations

Epigenetic changes allow environmental experiences to alter gene expression patterns that can be passed to future generations. Populations that survived historical famines, like Dutch communities during severe food shortages, show heritable genetic modifications that helped ancestors survive starvation. These changes may benefit descendants during food scarcity but could prove disadvantageous in modern abundant food environments.

Trauma also creates heritable epigenetic modifications. Refugee populations carry genetic changes inherited from parents who experienced traumatic events, even when the children never directly experienced the trauma themselves. These modifications represent the body's attempt to prepare future generations for similar environmental challenges, though their adaptive value in different contexts remains unclear.

9. Most genetic mutations are harmful, making beneficial changes rare

The vast majority of genetic mutations cause problems rather than improvements, with most deleterious mutations eliminated before embryos become viable fetuses. This explains why evolution typically requires extensive time periods to produce beneficial changes. However, when populations already carry genetic variation that becomes advantageous under new circumstances, evolution can proceed much more rapidly.

Standing genetic variation acts like a reservoir of potential adaptations waiting for the right environmental trigger. The most successful evolutionary changes often involve activating existing genetic variants rather than waiting for new beneficial mutations to arise. This principle explains how diving populations could develop their remarkable abilities relatively quickly by building upon genetic variation already present in human populations.

10. Gene editing raises complex ethical questions about human enhancement

The case of a Chinese scientist who used CRISPR to modify HIV receptors in babies sparked international controversy and ethical debates. The technology's current limitations, including off-target effects where unintended parts of the genome get modified, make it premature for human applications. However, as the technology improves, questions about enhancement versus correction become increasingly relevant.

The challenge lies in defining the boundary between treating genetic defects and enhancing normal human capabilities. Some conditions viewed as disabilities by society may not be perceived as problems by affected individuals. Additionally, expensive genetic screening technologies could create disparities where wealthy families gain advantages in selecting embryos with favorable genetic profiles.

The slippery slope from medical treatment to human enhancement raises questions about who decides what constitutes improvement versus normal human variation. These decisions will become increasingly important as genetic modification technologies advance and become more accessible.