Podcast Summary: Why are some people right (or left) handed?

Podcast: What's That Rash?
Host: ABC Australia
Episode Date: April 7, 2026

Episode Overview

This episode explores the topic of handedness—why most people are right-handed while a significant minority are left-handed. Hosts Dr. Norman Swan and Tegan Taylor discuss the science behind handedness, its presence in animals, the influence of genetics and environment, cultural attitudes, and whether training your non-dominant hand can improve brain function. The topic was sparked by a question from a World Science Festival Brisbane audience member about the potential cognitive benefits of using your non-dominant hand.

Key Discussion Points

Opening Conversation on Handedness (01:06–01:48)

• Hosts reveal their handedness:
  • Tegan: Left-handed
  • Norman: Right-handed
• Tegan shares that her immediate family has more lefties than righties, noting historical pressures on older relatives to switch to their right hand.

"There's three lefties to two righties in my immediate family..." — Tegan (01:19)

Prevalence and Animal Handedness (02:58–04:27)

• About 10% of humans are left-handed, a split that's been consistent across populations.
• Hand preference is also observed in animals:
  • A 2013 study found that 51% of 119 animal species studied had a preferred limb for tasks.
  • Other species have less dramatic splits (e.g., bees: 55/45; cats: roughly even).
  • Listeners learn how to test a cat’s paw preference!

"Bees have a preference, but it's about a 55, 45 split." — Tegan (03:27)
"You can test your cat's poorness if you want." — Tegan (03:43)

Evolutionary and Social Advantages (04:35–05:55)

• Human social learning may disadvantage lefties, but left-handedness offers advantages in situations where surprise matters (e.g., boxing, sword fighting).
• In sports, left-handed competitors often perform better than their 10% representation would suggest.

"Being a southpaw is an advantage. So it's a much higher than 10% success rate if you're a left handed boxer." — Tegan (05:25)

• Similar patterns noted in cricket and other sports.

Cultural Stigma and Myths (06:08–09:04)

• Left-handedness has been viewed negatively in many cultures.
  • "Sinister" originates from Latin for "left"; "dexter" (as in dexterity) means "right".
  • French: "gauche" (awkward, left) vs "adroit" (skilful, right).
  • Italian: "Mancino" (left-handed) comes from the word for crippled or defective.
• Myth-busting: Not all Scottish legends about left-handed "Kerrs" are true.

"So the word sinister means like crafty ... It's Latin for left, as opposed to the Latin word for right, which is dexter." — Tegan (06:12)

• Cultural pressure has led to the suppression of left-handedness, making data unreliable.

Forced Hand Switching & Its Impacts (09:04–09:55)

• Audience members recount being forced to write with their right hand at school.
• Such coercion was traumatic and may have contributed to stuttering, but mostly just traumatized children or made some ambidextrous.

"There was a theory for a while that it might have increased the risk of stuttering ... but it certainly was quite traumatic for a lot of kids." — Norman (09:19)

Defining and Measuring Handedness (09:55–11:35)

• Handedness isn't just about writing; it's evident in many tasks.
• Neurological dominance is assessed before certain brain surgeries via a series of everyday tasks.
• Brain imaging now supplements questionnaires to more accurately assess dominance.

"If you're pushing a broom, which hand is at the top... handed a pair of scissors... brushing your teeth..." — Norman (10:09)

Genetics and Environmental Factors (11:35–12:34)

• Multiple factors show a weak association with left-handedness: low birth weight, being a twin, season of birth (colder months), male sex, not being breastfed, left-handed mother.
• These factors combined have a very small effect size.
• The consensus: environment plays a stronger role, but the specific influences are unclear.

"The answer is it's almost certainly environmental, but they don't know what it is." — Norman (12:27)

Ambidexterity Explained (12:34–13:18)

• True ambidexterity is rare.
• Most people have a dominant hand even if skilled with both.
• Handedness exists on a spectrum, not a binary.

Myth-busting: "Training" the Non-Dominant Hand (13:18–14:56)

• Scientific studies show "brain training" by using your non-dominant hand does not lead to global cognitive improvements or protection against dementia.
• "Transfer" from such training is minimal; you just get better at the task you practice.
• Forcing ambidexterity (as was once done to school children) can have negative cognitive effects.

"No, all that happens when you do Sudoku is you get good at Sudoku." — Norman (13:23) "If you want to improve the little handed part on your other side of your brain, go for it. But it's not going to make you more brilliant...or stave off dementia." — Norman (14:50)

Key Takeaway

"Bottom line for Ian: don't bother, don't bother." — Tegan (14:56) "Stick with the hand that you've got, baby." — Norman (14:59)

Audience Q&A and Memorable Moments

International Left Handers Day (15:02)

• August 13th is International Left Handers Day.

Audience Mailbag: Mediterranean Diet (15:27–18:29)

• Question: Is non-alcoholic red wine as healthy as red wine in the Mediterranean diet?
• Norman clarifies: Alcohol isn't a necessary component of the Mediterranean diet; health benefits come more from food diversity and cooking methods (notably how tomatoes' nutrients are made more bioavailable by chopping/dressing/roasting with olive oil).

"It turns out with the diet that it's the way you cook it, it's the dietary pattern, it's the cuisine as much as the components." — Norman (18:05)

Listener Story: Testing Cat Handedness (18:29–19:11)

• Listener Natalie reports her cat Aurora was uninterested in the "paw preference" test, proving cat behaviour is as unpredictable as ever.

Notable Quotes & Moments

• On left-handed boxers and the advantage of surprise:
  "Being a southpaw is an advantage... it's a much higher than 10% success rate if you're a left handed boxer." — Tegan (05:25)
• On cultural bias:
  "Our word for not left is literally right." — Tegan (06:54)
• On brain training:
  "No, all that happens when you do Sudoku is you get good at Sudoku." — Norman (13:23)
• On cat preferences:
  "If you would like to know what paw your cat prefers to use... you can see which one of its dainty little paws it puts in to get the treat..." — Tegan (04:07)
• On forced handedness:
  "It traumatised a lot of children." — Norman (09:19)
• Final advice:
  "Stick with the hand that you've got, baby." — Norman (14:59)

Conclusion

This episode demystifies handedness, dispelling myths about its genetic inevitability and cognitive consequences. The hosts reaffirm that forcing yourself to use your non-dominant hand won’t stave off dementia—stick to what feels natural! Listeners also enjoy asides about cat behaviour, left-handed sports, and the nuances of the Mediterranean diet.

For more answers to your health questions, submit an email to the show or listen to related episodes on alcohol and the Mediterranean diet.