The Jordan Harbinger Show

1272: Left-Handedness | Skeptical Sunday

January 18, 2026

Key Takeaways Copied to clipboard!

  • Left-handedness (affecting about 10% of the population) is determined by a complex interplay of genetics (like the TUBB4B gene variant), prenatal environment (such as maternal age and in-utero positioning), and random developmental quirks. 
  • Left-handed individuals often exhibit neurological differences, including a larger corpus callosum, which may correlate with advantages in multitasking, creativity, and higher IQ scores, but also potentially higher rates of dyslexia and insomnia. 
  • Cultural conditioning and historical taboos have significantly impacted left-handed individuals, ranging from forced hand switching in schools to social customs where the left hand is considered unclean for eating due to its historical association with hygiene duties. 

Segments

Introduction to Left-Handedness
Copied to clipboard!
(00:00:00)
  • Key Takeaway: The episode of The Jordan Harbinger Show, 1272: Left-Handedness | Skeptical Sunday, begins with sponsor messages before introducing the topic of left-handedness.
  • Summary: The episode opens with advertisements for LinkedIn and then transitions into the Skeptical Sunday format. Host Jordan Harbinger introduces co-host Jessica Wynn to discuss the science behind being left-handed. The initial discussion highlights common frustrations for lefties, such as poorly designed scissors and spiral notebooks.
Causes of Handedness
Copied to clipboard!
(00:03:35)
  • Key Takeaway: Handedness is a result of genetics, environment, and random brain development quirks, with no single determining gene.
  • Summary: Left-handedness is not caused by a single gene but a cocktail of small influences, affecting only about 10% of the global population. Men are slightly more likely to be left-handed than women, and children born to mothers over 40 show a higher likelihood of being left-handed. This prenatal influence is theorized to relate to hormone exposure affecting brain development in the womb.
Brain Asymmetry and Genes
Copied to clipboard!
(00:05:43)
  • Key Takeaway: Brain asymmetry, which dictates handedness, is set early in utero, often involving language centers being located in the left hemisphere controlling the right hand.
  • Summary: The left-right split in brain hemispheres is established early, often determining handedness before birth. A rare gene variant, TUBB4B, linked to microtubules that scaffold neuron growth, is found mutated more often in left-handers, influencing the fluid flow that creates this brain asymmetry. Identical twins can still have different dominant hands, confirming that environment and random development play a significant role.
Womb Position and Development
Copied to clipboard!
(00:09:16)
  • Key Takeaway: Fetal position in the womb and early thumb-sucking preferences observed as early as 10 weeks predict lifelong handedness.
  • Summary: Tiny random differences in a fetus’s position in the womb, such as head turning bias, can influence which hand becomes dominant later in life. Ultrasound studies show fetuses exhibit consistent hand movements by 18 weeks, with thumb-sucking preference correlating to future handedness. This suggests handedness is decided before the thumbs fully develop.
Heredity and Environmental Influence
Copied to clipboard!
(00:10:44)
  • Key Takeaway: While children of left-handed parents are more likely to be left-handed, heredity does not guarantee it, and cultural conditioning can force adaptation.
  • Summary: Heredity raises the odds of a child being left-handed but does not seal the deal, as evidenced by identical twins having different dominant hands. Post-birth, cultural factors like imitation and forced switching (historically seen in schools) can influence hand dominance. The host shared a personal anecdote of being forced to write right-handed by nuns, resulting in poor penmanship.
Cultural Taboos and Hand Use
Copied to clipboard!
(00:20:00)
  • Key Takeaway: Historical and cultural taboos, often rooted in religious or conformity pressures, have led to the left hand being associated with uncleanliness or evil.
  • Summary: Historically, left-handed writing was sometimes viewed as an affront to divine order, and in some societies, using the left hand for eating remains rude because it was traditionally designated for bathroom hygiene. This cultural conditioning, rather than religion alone (as seen in former East Germany’s push for conformity), can influence or suppress natural handedness.
Cognitive and Athletic Advantages
Copied to clipboard!
(00:26:24)
  • Key Takeaway: Left-handers’ larger corpus callosum facilitates faster communication between brain hemispheres, potentially leading to advantages in multitasking and creative fields.
  • Summary: Left-handed people often have a larger corpus callosum, the bridge connecting the brain hemispheres, enabling faster information processing and better multitasking abilities. This increased interhemispheric connection is linked to higher representation in creative fields and studies showing more left-handers scoring over 140 IQ points. Furthermore, lefties process language using both hemispheres, unlike most right-handers who primarily use the left.
Athletic Dominance and Southpaw Origin
Copied to clipboard!
(00:32:05)
  • Key Takeaway: Left-handedness provides a distinct evolutionary and competitive advantage in one-on-one sports because opponents are less prepared for the angle of attack.
  • Summary: Left-handed athletes dominate sports like boxing, baseball, and tennis because their stance confuses right-handed opponents who are trained for conventional angles. The term ‘southpaw,’ often associated with left-handed pitchers, originated in boxing slang from the 1800s, linking ‘south’ (left) with ‘sinister’ (evil), before being popularized by baseball.
Astronauts, Vision, and Animal Handedness
Copied to clipboard!
(00:38:39)
  • Key Takeaway: Left-handed individuals are disproportionately represented among astronauts and show superior vision when submerged underwater.
  • Summary: Approximately 60% of astronauts are left-handed, possibly due to factors related to brain lateralization affecting vision and hearing, which also benefits underwater divers who see better with their left side favoring. Handedness is a widespread phenomenon across the animal kingdom, seen in cats, dogs, chimpanzees, and even the shell coiling direction of snails, all pointing to brain lateralization.
Health Correlates and Conclusion
Copied to clipboard!
(00:44:02)
  • Key Takeaway: Left-handers tend to hit puberty later, report more vivid dreams, and show a higher correlation with alcohol consumption and immune disorders.
  • Summary: Health correlations suggest left-handed boys reach puberty about a year later than their right-handed peers, and nail growth is faster on the dominant hand for everyone. The increased brain communication in lefties may also lead to more vivid dreams but a higher propensity for insomnia. Ultimately, handedness is a complex outcome of genetics, environment, and chaos, highlighting the wonderful weirdness of the human brain.