Dr. Melissa Ilardo: How Our Lives Shape Our Genes
Superhuman abilities aren't confined to comic books. Dr. Melissa Ilardo, a professor of Biomedical Informatics at the University of Utah, finds them in the real world.
Her research reveals how extreme lifestyles drive rapid evolution, from the Bajau sea nomads with genetically enlarged spleens to the Haenyeo divers of Korea.
This is a look at evolution in action—and what these remarkable adaptations reveal about our own biology.
Table of Contents
The Sea Nomads of Southeast Asia
Genetics, Behavior, and Human Variation
The Cognitive Gifts of Neurodiversity
The Ethics of Genetic Engineering
The Sea Nomads of Southeast Asia
Survival and Adaptation
The Bajau live on the ocean and dive deep for food, with extraordinary breath-holding abilities. They perform strenuous dives to 100 feet or more, with tales of 13-minute breath holds that rival professional records. Their lifestyle is so intertwined with water that children often learn to swim before they walk.
This lifestyle is a stark filter for genetic fitness. Free diving is inherently dangerous; competitive free divers often pass out and require rescue, a luxury not available to the Bajau in the open ocean.
For them, those who cannot adapt often perish before they can reproduce. Conversely, those with genetic variations that allow them to excel at diving are more likely to survive, provide for their families, and pass on those traits.
A Biological Scuba Tank
Dr. Ilardo’s research team discovered that the Bajau have spleens roughly 50% larger than neighboring land-dwelling populations.
The spleen acts as a “biological scuba tank,” storing oxygenated red blood cells. Triggered by the dive reflex—a response to cold water on the face—the spleen contracts, releasing a reservoir of oxygen-rich blood and providing an oxygen boost of up to 10%.
This enlarged spleen was observed in both divers and non-divers, suggesting a genetic component. Further research revealed a gene variant in the Bajau that correlates with higher thyroid hormone levels, a mechanism confirmed in mice to lead to larger spleens.
Superior Underwater Vision
The Bajau and Moken people now use goggles, but this is a recent development. A study with Moken children showed they had superior underwater vision compared to European children.
While water normally blurs vision, it’s suggested the Moken children could constrict their pupils to an exceptionally small size, creating a pinhole camera effect. It is believed a genetic component likely contributes to this visual prowess.
Genetic Advantage in Athletics
This phenomenon of super-performance extends to other areas. Marathon runner Eliud Kipchoge’s record-breaking achievements, along with the fact that many elite endurance runners come from specific regions like the highlands of Ethiopia, suggest inherited traits.
These may include red blood cell characteristics, bone structure, or adaptations to altitude, which, combined with training, could explain their superior performance.
The Haenyeo Sea Women
The Haenyeo are a group of female divers in Korea whose practices offer fascinating insights into cardiovascular health. This all-female diving population on Jeju Island has been active for potentially thousands of years.
The tradition is now in decline; the average age is over 70 because fewer young women are choosing the physically demanding diving life, opting instead for careers in the city.
Diving Practices and Health
Remarkably, the Haenyeo traditionally dived in extremely cold water wearing only thin cotton suits. They continue diving throughout their pregnancies, often returning to the water just days after giving birth.
This presents a unique scenario where natural selection can act on two generations simultaneously. Their dives to depths of around 10 meters (30 feet) are significant, especially for divers in their 70s and 80s.
Pregnant women with sleep apnea, a form of unintentional breath-holding, are at increased risk for hypertensive disorders like preeclampsia.
The Haenyeo, however, possess a genetic variant that lowers their diastolic blood pressure during dives, potentially protecting them from these dangerous conditions. Insights from their biology could help develop new therapeutics for pregnant women.
Cultural Significance
The Haenyeo are incredibly tough, with some diving past the age of 100. Though perhaps marginalized in the past, they are now deeply respected and recognized as a UNESCO Intangible Cultural Heritage of Humanity, a status that highlights the urgent need to safeguard their traditions. They practice sustainable harvesting of resources like sea urchin, abalone, and octopus, prioritizing the health of the marine environment.
Diet as a Driver of Evolution
The powerful drive for humans to acquire protein and fat, especially in combination, has been a significant force in evolution. The great lengths some populations go to—even risking their own lives and those of their unborn children, often in frigid environments—underscore the biological importance of these nutrients.
This quest for specific foods has driven the selection of genes. Two clear examples illustrate the potent influence of diet on natural selection:
Lactase persistence—the ability to digest milk into adulthood—evolved rapidly and independently in diverse populations across Africa and Europe.
The Greenlandic Inuit, whose high-fat diet of marine mammals led to genetic adaptations for better lipid metabolism.
Genetics, Behavior, and Human Variation
The age of epigenetics has revealed a profound truth: our genes are not our destiny. While some traits are fixed, our capacity for change is greater than previously thought.
This challenges the classic evolutionary diagram of a quadrupedal animal evolving into an upright Homo sapiens, which implies a linear trajectory with humans as the pinnacle.
The irony is that modern humans are often found hunched over their phones, resembling earlier primates. The reality is that evolution is not about achieving a perfect state, but about fitting an environment.
Gene Expression and Timelines
While traditional Mendelian genetics, like the inheritance of eye color, suggest some traits are set, behavior and environmental pressures can influence gene expression much more rapidly. Genetic changes occur on different timelines.
Gene expression can shift in minutes or hours based on environmental stimuli, and these epigenetic modifications can be passed down through generations. For example, the inherited metabolic effects of a famine on a Dutch population centuries ago can be disadvantageous in a modern world of abundant food.
Changes to the genes themselves, through mutation or population variation, were once thought to take thousands of years. We now understand this can occur more quickly, perhaps within a millennium or two.
Hybrid Vigor and Human Variation
The increasing diversity seen in media, where interracial couples are now common, reflects a broader trend of genetic admixing. This mixing of different ancestral populations is a key source of human variation.
While this variation can confound genetic analyses, it does not mean humans are diverging into separate species. Even significant physiological differences, like eye color, can stem from minute genetic variations. No human population shows the level of divergence required for speciation.
This mixing often leads to "hybrid vigor," where offspring from genetically diverse parents show enhanced resilience. Conversely, incest increases the risk of inheriting two copies of a detrimental gene, which is why nature has built-in systems to discourage reproduction between close relatives.
Accelerated Adaptation
Evolution is often asymmetrical: it takes many generations to evolve a trait, but very few to lose one. This is partly because most mutations are harmful and often go unseen, as they can result in early mortality or non-viable embryos.
However, adaptation can be accelerated by "standing variation"—pre-existing genetic diversity within a population. When a previously neutral trait becomes advantageous in a new environment, it can be selected for quickly.
The Tibetan high-altitude adaptation is a prime example. This trait is believed to have originated from interbreeding with Denisovans, another hominid group, which essentially allowed humans to "steal" advantageous genes. While the gene likely existed before, it only became widespread when Tibetans migrated to high altitudes.
Research by Svante Pääbo has confirmed interbreeding with both Neanderthals and Denisovans was relatively common, even discovering a first-generation offspring of a human and an archaic hominid.
Genetic Quality Control and Physical Signs
Miscarriages can be seen as a form of nature's quality control, weeding out mutations that would be detrimental. Many mutations result in non-viable embryos, leading the genetic program to halt early in development.
This raises the question of whether there are physical markers for internal adaptations. Physicians have noted correlations between wine-spot birthmarks and potential internal organ mutations.
Similarly, in diving populations, it remains unclear if their incredible fitness is due purely to lifestyle or if external markers could indicate internal advantages like hypoxia resistance. The phosphodiesterase gene in the Bajau, for instance, is involved in numerous functions, meaning a mutation could have widespread effects.
Genetics and Mate Selection
Conscious and unconscious preferences, like smell, can be tied to genetic compatibility. It’s plausible that seemingly unrelated traits—such as spleen function and hand shape—could be genetically linked, influencing our mate choices without our awareness.
While traits that improve diving are likely selected for, it's possible they also inadvertently increase attractiveness through sexual selection.
Immunity and the Benefits of Water
There is interest in whether practices like cold water face immersion, which triggers the dive reflex, could boost immune function. While clinical trials are lacking, the robust health of older diving populations raises questions.
At a minimum, water activities like swimming are excellent low-impact exercises, sustainable ways to maintain fitness well into old age. The historical importance of oceans as a food source suggests coastal populations might be more likely to carry genetic variations related to diving, though evidence of diving near inland river systems suggests a broader human connection to water.
The Cognitive Gifts of Neurodiversity
Adaptation extends from physical to cognitive performance. Individuals with conditions like schizophrenia and autism can possess remarkable abilities, such as exceptional calculation skills, sparking discussion on how genetics might influence these gifts.
There is a known correlation between people in STEM fields and having family members with autism, pointing to the advantages of traits like hyperfocus.
Oliver Sacks’ work on Tourette's syndrome also noted faster processing speeds. Conditions like prosopagnosia (face blindness) are often correlated with a "nerdy, quirky phenotype," highlighting the complexity of pathologizing such traits.
This raises the question of whether it's better to specialize or remain a generalist. The documentary Spellbound shows how intense training in one skill can sharpen it while potentially limiting others.
However, we must guard against genetic determinism. Studies on mindset show that subjects who were told they were genetically predisposed to improve with training did, in fact, perform better—regardless of their actual genes.
This complexity is underscored by anecdotes, such as an adopted family member having exceptional rhythm despite no known genetic link to it in the adoptive family.
The Ethics of Genetic Engineering
The conversation about genetics inevitably leads to the ethics of engineering our own evolution. A scientist in China who used CRISPR to modify the genomes of babies sparked international criticism and a global pause on such research.
While CRISPR holds promise for preventing diseases like Huntington's, it remains an imprecise tool with the risk of "off-target" effects. This raises the complicated question of who decides what constitutes a "defect" versus an enhancement.
A thoughtful analogy illustrates the dilemma: if a genome indicates a baby will be born blind, should that be considered a "problem" to be fixed?
As whole-genome sequencing becomes more affordable, new questions arise about accessibility and disparity based on socioeconomic status.
The discussion provides a sharp contrast to selective breeding in animals—for example, a Bolognese dog bred solely for cuteness and companionship—highlighting the profound ethical stakes of human genetic engineering.
Wrapping Up
The journey from the sea nomads to the genetics lab reveals a powerful truth: human evolution is not a relic of the past, but an active, ongoing process.
Our genes are in constant dialogue with our environment, diet, and behavior, shaping everything from physical endurance to cognitive function.
As we gain the power to consciously engineer our biology, we move from being subjects of evolution to its potential authors. The ultimate question is no longer how we adapt, but how we choose to.