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

KEYPOINTS

• 01

  Gene expression responds to behavior and environment on several timescales

  Ilardo, a geneticist at the University of Utah, describes changes that happen within minutes or hours as genes respond to stimuli, and slower epigenetic marks (molecules attached to the genome) that can be passed to children. She cites refugee populations carrying inherited marks from events their children never experienced, and famine signatures in Dutch populations. Those marks may help survival during scarcity but could be maladaptive once food is abundant.

• 02

  Natural selection moves fastest when useful variation is already present

  Most new mutations are harmful, and many produce non-viable embryos that are never seen. Waiting for a brand-new beneficial mutation can take a very long time. Rapid human adaptation usually draws on 'standing variation': differences that sit quietly until a group moves into a new environment or takes up a new behavior, such as breath-hold diving.

• 03

  Some of the biggest human adaptations came from mixing with other groups

  The Tibetan high-altitude adaptation is thought to come from interbreeding with Denisovans more than 10,000 years ago. The variant only became strongly advantageous once Tibetan ancestors moved to very high altitudes. Ilardo argues that today's globalized mixing creates gene combinations never seen before, bringing both new resilience and new disease risks. In her view humans have not stopped evolving.

• 04

  Smell may track immune-gene differences in potential mates

  In the sweaty T-shirt studies discussed, people rated the scent of opposite-sex strangers. They preferred the odor of people whose major histocompatibility complex (immune) genes were most different from their own. The proposed logic is offspring with a broader immune repertoire. Huberman notes these are not pheromone effects. The same logic explains why nature penalizes inbreeding: close relatives are more likely to share harmful recessive variants.

• 05

  The mammalian dive reflex is triggered by breath holding with a cold face

  Holding your breath with your face in cold water makes your heart rate slow and blood vessels in the limbs constrict, keeping oxygenated blood central for the brain. The spleen also contracts. Lab protocols use water at about 10 °C (50 °F) for as long as the breath hold lasts. Vagal nerve stimulation through the face appears important, though breath holding alone contributes. The reflex exists across mammals, including trained diving mice.

• 06

  Splenic contraction releases stored red blood cells and gives about a 10% oxygen boost

  The spleen acts as a reservoir of oxygen-carrying red cells, sometimes called a 'biological scuba tank'. Ilardo puts the boost at around 10% in most people. However, the spleen takes those cells back after the breath hold ends, so the boost is temporary. Spleens also contract somewhat during exercise, which may be why horses and greyhounds have large spleens.

• 07

  The Bajau sea nomads have spleens about 50% larger than nearby farmers

  Ilardo compared the Bajau of Indonesia with a nearby coastal population that farms and often cannot swim. Bajau spleens were roughly 50% larger on average, and this held for non-divers as well as divers. That points to genetics rather than training. Whether diving itself enlarges the spleen remains open: trained volunteers in other studies did show larger spleens.

• 08

  A selected variant links higher thyroid hormone to bigger spleens and more red cells

  The gene evolving in the Bajau correlates with higher-than-average (not clinically hyperthyroid) thyroid hormone levels. Europeans carrying the same variant also had higher thyroid levels and larger spleens. In mice carrying the change, spleens were larger but less dense, with higher hemoglobin, hematocrit and red cell counts. EPO levels did not change, which makes this an EPO-independent route to more red blood cells.

• 09

  Korea's Haenyeo divers show one trained adaptation and one genetic adaptation

  These all-female divers on Jeju Island have an average age of about 70 and dived in cotton suits until the 1980s, often through pregnancy. Trained divers showed an exaggerated slowing of heart rate on diving, which non-divers with the same genetics lacked. One diver dropped more than 40 beats per minute in under 15 seconds. Separately, a genetic variant lowered their diastolic blood pressure during dives.

• 10

  Gene editing of embryos is still a blunt and ethically unresolved tool

  Discussing the Chinese researcher who used CRISPR to edit babies' genomes, Ilardo notes off-target edits as a key technical problem, though the field is improving quickly. The harder question is where correction ends and enhancement begins. Some traits labeled defects are simply human variation to others, and it is unclear who would decide.