← What's That Rash?
What's That Rash?
Why are some people right (or left) handed?
00:20:09
What determines whether you’re right or left handed? Is there really such a thing as being ambidextrous? It’s a surprisingly complicated story, and culture comes into play – some people are forced to go against their dominant hand. Norman and Tegan parse through the history of handedness in this live recording at the World Science Festival Brisbane. References: A large-scale population study of early life factors influencing left-handedness The handedness of Kerrs and Carrs The association between switching hand preference and the declining prevalence of left-handedness with age Stuttering and “Retraining” Left-Handed Children in Mid-Century U.S. Can training to become ambidextrous improve brain function? Brain Size Associated with Foot Preferences in Australian Parrots The Influence of Handedness on the Clinical Presentation and Neuropsychology of Alzheimer Disease If you enjoyed this episode, check these out! Can sudoku really keep your brain younger for longer? Should y...
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- [00:01]
Tegan
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- [01:06]
Norman
I've never noticed. Tegan, are you right handed or left handed?
- [01:09]
Tegan
Well, you never see me right because we're never in the same room as each other. I am left handed. How about you?
- [01:14]
Norman
I'm right handed.
- [01:15]
Tegan
You're always right.
- [01:16]
Norman
So lots of people in your family left handed or is it just you?
- [01:19]
Tegan
It's actually we outnumber the right handed people in my immediate family. There's three lefties to two righties in my mum, dad, me and my two sisters and my grandmother on one side and my grandfather on the other side were also both left handed but were very much encouraged to not be left handed by the people in their lives because it was the time that they grew up in.
- [01:40]
Norman
Yeah, they got whacked like my father did in school to force them to write with their right hand. Anyway, handedness is what we're talking about today on what's that Rash?
- [01:49]
Tegan
It's the show where we answer the health questions everyone is asking. And this was a question that we answered at our recent live show at World Science Festival Brisbane. Hi, I'm Ian and many years ago I was working with a colleague who was struggling to use his computer mouse. When I asked him about it, he said that he was deliberately using his left hand even though he was right handed. His theory was that it forced the brain to use different neural pathways and thus kept it fresh, hopefully staving off dementia in old age. Is there any truth to this theory, Ian? You couldn't have done a better job of reading that out. Thank you so very, very much.
- [02:32]
Norman
Given the computer age, I actually don't know. Are you right handed or left handed?
- [02:35]
Tegan
I am left handed. What are you?
- [02:38]
Norman
I'm right handed.
- [02:40]
Tegan
All right, who's with me? Left hand's up.
- [02:43]
Norman
Oh, good.
- [02:44]
Tegan
Really? Okay, cool. Add right handed people. Yeah, that's what we thought. Is anyone here ambidextrous? Yes, we'll be the judge of that in a while.
- [02:55]
Norman
You might not want to be ambidextrous, but I'm going to tell you what the story is. But anyway, that's not a story.
- [02:59]
Tegan
So this is actually a pretty representative sample because about 10% of humans are left handed. It's not the same across species, though. Yes, other species are, have handedness or have preferences as to which limb they use. So there's a study in 2013 that compared 119 different animal species, ranging from toads and lizards to birds and primates, and found that 51% of the species had a preferred limb when doing a fine motor task. But it's not the same split among species. So, yeah, we've got this 9010 split in humans. Quite dramatic. Bees have a preference, but it's about a 55, 45 split. That's according to research from here in Queensland at the University of Queensland. Cats have a preference generally, but it's a pretty even split. But you can test your cat's poor ness if you want. You hate cats, don't you, Norman?
- [03:58]
Norman
I do.
- [03:59]
Tegan
If you're a cat lover, please hiss at Norman now if you like.
- [04:04]
Norman
This comes from our producer Shelby, who's a cat lover.
- [04:07]
Tegan
If you would like to know what paw your cat prefers to use, what you can do to test it is get like an empty toilet paper roll. Like a toilet roll. And you can put a little treato in the bottom of it and you can see which one of its dainty little paws it puts in to get the treat because it can only fit one paw in. So, yes, cat's handedness very evenly split human's handedness.
- [04:27]
Norman
Elephants, how they use their trunks and
- [04:29]
Tegan
things like that, I don't know. I wasn't part of the research study that looked at the. I don't have all 119 species here, unfortunately.
- [04:35]
Norman
Do we know what the evolutionary advantage is?
- [04:38]
Tegan
It's okay. So, so, yes.
- [04:40]
Norman
So humans, I'm glad you got that.
- [04:43]
Tegan
Humans are a really social species and we have been able to dominate this entire planet and potentially the rest of the solar system because of our ability to work together. And so working together means teaching each other the skills that we have. And it's easier to Teach the skill. If you're a left handed person, you know exactly what I'm talking about. It's easier to teach a skill to someone who has the same preferred hand as you. Which means that having left handedness should be an impediment to survival. But the elements of surprise is also quite powerful. So if you look at professional boxers, like fighters, what you'll see through almost every tier of eliteness.
- [05:24]
Norman
It's called the southpaw, isn't it?
- [05:26]
Tegan
Yeah, being a southpaw is an advantage. So it's a much higher than 10% success rate if you're a left handed boxer. Because if you're a right handed boxer, pretty much everyone you're ever punching is punching you back with their right hand. And you get pretty good at punching people with your right hand. But if you are left handed, then you have the element of surprise on your side. But it only works if it's a surprise. So that's why around that 10% seems to have been pretty stable across populations.
- [05:52]
Norman
And bowlers always complain about bowling to a left handed cricket batsman.
- [05:56]
Tegan
Exactly. So you can, if you're in that school, minority with me, that's, that's part of the reason why. But because humans are such a social species that's selected for in that really dramatic way. Other species less so.
- [06:08]
Norman
But there's all this cultural stuff. You know the word sinister.
- [06:12]
Tegan
Exactly, exactly. No, Very, very good. So if you look at different languages. So the word sinister means like crafty. Yes, exactly. So we think of that word as having connotations of untrustworthiness. It's Latin for left, as opposed to the Latin word for right, which is dexter. Dexter as in dexterity, as in being skilled at something like that. It's the word for skillful. Similarly in French, gauche, as in something that we would think of as being maybe like tacky. Left adroit, which we would say is a skilful right. Latin mancino, Mancino, which is derived from the word for crippled, maimed or defective, is left. And then in English, obviously our word for not left is literally right. So it is one of these things that has been mistrusted. In fact, actually, Norman, I want to fact check something with you. As a Scotsman. Yes, apparently. Verify this for me. Is it bad luck to meet a left handed person at the start of a journey?
- [07:19]
Norman
I've never thought so. But maybe there's some Highland.
- [07:23]
Tegan
This is something that you've been brewing
- [07:24]
Norman
since the day we met this family. The Scottish family cares who are supposed.
- [07:28]
Tegan
Yes. Okay, so we will talk about the genetics in a second. We will talk about the genetics in a second. But because it's not just genetic, but there was a family clan Cur in Scotland, typically associated with left handedness. There's a castle which belonged to the family, which supposedly has a turnpike stairs explicitly designed with left handers in mind. It's now on my bucket list. But there was a couple of people in this family that were left handed swordsmen and it became an advantage. A bit like the boxers, right? A left handed mercenary could command a higher fear for his services and people who fought that way were called cur handed. So that's where it ended up being kind of associated with this particular family. However, in 1972 the British Medical Journal went and looked into this family, said 30% of people with the surname Kerr were left handed compared to 11% of the world's population. But that was pretty much debunked in 1993. So if you have a, if you're a Kerr or, you know, a Kerr and they're left handed, could just be confirmation bias or maybe there's something to it.
- [08:38]
Norman
There's, you know, sitting to the right of the king or sitting to the right of God and, and the right hand being the clean hand, the left hand being the dirty hand.
- [08:45]
Tegan
That's true. So in some cultures it's sort of reinforced by culture, which I guess goes to this idea that some people, up until probably a generation or two ago and maybe still in some parts of the world, it's really hard to get good statistics on handedness because people were sort of funneled into using their right hand, whether that was their preferred hand or not.
- [09:04]
Norman
So was anybody here forced to try and use your right hand really at school? Yeah.
- [09:11]
Tegan
Do you want to talk about what could have happened to those people in their poor little brains? Didn't work. Yeah. Okay.
- [09:19]
Norman
Well, there's a lot of, I mean it traumatised a lot of children. You know, in Scotland you used to get the belt or banged over your wrist. There was a theory for a while that it might have increased the risk of stuttering because of the nervous reaction of children. They're not so sure about that, but it certainly was quite traumatic for a lot of kids. And it comes to that sort of brain training thing, which we'll come back to later, but. But it mostly didn't work or made people ambidextrous. People that worked a little bit, it never made them right handed, but it made them ambidextrous. Such was the prejudice against Left handed people.
- [09:55]
Tegan
So we need to talk about ambidextrousness now because I think, well, maybe before we do that, we talk about how like you put your hand up if your left hand, you put your hand up if you're right hand, ambidextrous, that's based on the hand you write with. Correct. But there's more to it than that.
- [10:09]
Norman
There is. So before you have major neurosurgery, certain kinds of neurosurgery, or you're having an operation, say for brain cancer, the neurosurgeon needs to know which is your dominant side, the dominant hemisphere. And that goes partly to your handedness. And so there's various questions that they ask you. So some of you might think that you're right handed, but you may be left handed or significantly left handed. So the common thing is do I write with my right hand? But the question is if you're pushing a broom, which hand is at the top of the broom? If it's your left hand rather than your right hand. If you're right handed, it's going to be your right hand. But if you've got a tendency to left handed, you might put your left hand at the top of the broom. If you're handed a pair of scissors, do you cut with your right hand or your left hand? So people who write with their right hand may cut with their left hand. When you're brushing your teeth, do you use your right hand or your left hand? And there are also brain scans that they can do now. But when you do these, and there's a whole series of these questions as well as the brain scans, you sometimes get a surprise. And that's why they started asking all these questions, because they would do surgery on people and discover they've operated on the dominant lobe, not realizing it was the dominant lobe and causing problems.
- [11:21]
Tegan
So they're looking in the brain or hemisphere, I should say they're looking at people's preferences. And it obviously isn't just sort of like a switch of one or the other or what do we know about the drivers of handedness?
- [11:36]
Norman
Well, not a lot. Well, so when I say not a lot, there have been quite big studies looking at the genetics of it and the factors. So low birth weight, child born, low birth weight. There is an increased tendency to left handedness in that child. Multiple births, twins and triplets, increased tendency to left handedness. Season of the year, colder months, born in the colder months, more likely to be left handed. Males more than females, not being breastfed for some reason. And a mother who is left handed is more likely to have a baby that is left handed. But when you add all those up, they don't amount to very much. In other words, what statisticians call the effect size. The effect size of all these variables is tiny even when you add them up. So the answer is it's almost certainly environmental, but they don't know what it is.
- [12:35]
Tegan
So we talked about ambidextrousness before, and one of the things that I wanted to call out about that is that you can think you're ambidextrous and not be so. His handedness is along a spectrum. And when someone is considered to be ambidextrous is when they are ambidextrous, as in they're like equally dexterous, remembering that the word comes from the word for right in Latin. They're equally able to use both sides of their body. And actually most people aren't. They can be very skilled in both sides, but still have a preferred dominant hand. So to come to the question. So the question really wasn't about handedness at all. It was about forcing yourself to use your non dominant hand to amplify your brain power somehow. Is there anything in that?
- [13:18]
Norman
So I need to talk about something called transfer. You know, if you're buying a cognitive training program or what have you, or you're doing Sudoku, what you're hoping is that by doing Sudoku that makes your brain more developed or has more resilience, and therefore in all your other activities of daily life, it's going to be better. No, all that happens when you do Sudoku is you get good at Sudoku. So whichever part of the brain is the Sudoku, part of your brain, you know, enlarges when you do Sudoku, but nothing much else happens. And this is called transfer. So most of people who do cognitive training, and this is the implication in the question, is that if I force myself to use the other hand, am I developing my whole brain and is it going to transfer to other things in my life? And it turns out that if you actually do that and force this, it's been done in non human primates, you do get a brain effect, but it's like doing Sudoku, it's just in a very small part of the brain and there's no transfer. And when you look at a situation when it's been forced and you look at people who, in the old days, who were actually trained, forced to try and do that and became ambidextrous, in fact, there was some decline in cognitive function. So it was actually damaging to do that to children. So there was a negative effect on the brain. Now these are not big studies, you can't go to town on it, but there wasn't an improvement. And that's the best that you can say is that 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 in the rest of your life or stave off dementia.
- [14:57]
Tegan
So bottom line for Ian, don't bother, don't bother.
- [14:59]
Norman
Just stick with it. Stick with the hand that you've got,
- [15:03]
Tegan
baby, and you can all put it in your calendars. International Left Handers day is Thursday 13th August. High five a left handed person that day and please thank Norman with the sound of one hand clapping. So Norman, we also obviously always do our mailbag here on WhatsApp rash. And at the live show at World Science Festival Brisbane, we did a live mailbag. AKA people in the audience were able to ask questions.
- [15:27]
Norman
Hi, I've just got a question. And it's to do with the Mediterranean diet.
- [15:33]
Tegan
Well done.
- [15:35]
Norman
Australians in general, as they're getting younger, they're looking more and more of moving away from alcohol. Part of one of the joys of the Mediterranean diet is that lovely glass of red that you could have with dinner. Is there still the advantage of having a glass of non alcoholic red with your dinner as opposed to. And are there any other parts of the diet perhaps where you could look at alternative options that are in the diet itself?
- [16:09]
Tegan
Right before you get started, I do want to refer people to the episode of what's that rash we did saying is a little bit of alcohol. Can a little bit of alcohol be a good thing for you? I think it's one of our most complained about episodes because I think we called red wine drinkers tosses, but both of us would identify as such. So having said that, that's because, you
- [16:29]
Norman
know, I drink red wine. So the answer is alcohol is not as much part of the Mediterranean diet as you think.
- [16:36]
Tegan
Get it out of your system. Just go down.
- [16:40]
Norman
The question is, is a red drink made from grapes good for you? So the answer is the red drink or any alcohol. But there's no. When you look at the studies with alcohol, there is no benefit from the alcohol, the red wine or white wine itself. Now it could be that's the alcohol counteracting the effects of wine. However, red is a good color in a diverse diet because it's got lycopenes and so you tend to have more antioxidants in the red color, but you've got rainbow colors in food and all the colors mean that you've got bioactive compounds in it. So it could be that grape juice has antioxidants and bioactive compounds in it. But really most of that's going to come from the vegetables in your diet. It's not that much fruit in a Mediterranean diet, but the vegetables in it and how you cook them. So for example, if you take a tomato and this is work done at Deakin University, if you take a tomato and instead of eating some rubbish, a raw tomato is great. If you chop the tomato, it releases more bioactive compounds. Pour dressing on it and it may be the vinegar that's as active as the olive oil. Then you release even more. There's a chemical reaction. But here's the magic. If you roast a tomato with olive oil, it really does produce massive amounts of bioactive compounds. And 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 of the diet.
- [18:21]
Tegan
In addition to our red wine episode, we have also done an episode on the Mediterranean diet which is worth re listen.
- [18:29]
Norman
And after the show an audience member emailed us.
- [18:32]
Tegan
Yeah, they emailed about. So I'd given some directions on how to figure out if your cat is left or right handed. And Natalie emailed in saying loved seeing what's that rash in person today. Natalie, thank you for coming to our show. I tried Tegan's directions to attempt to work out which is Aurora's dominant paw by putting a treat in a toilet roll. But Aurora did not play along. I guess I'll just have to live without knowing this very important trait. And Natalie has attached a couple of photos of a very cute grey cat not putting her paw inside the toilet roll to get it through.
- [19:05]
Norman
Very cat like behaviour, if I might say so as a cat, no one wants to see what I mean.
- [19:11]
Tegan
Everyone knows you hate cats, normal. You don't have to hide it anymore. Well, thank you Natalie and everyone who came to our show at World Science Festival Brisbane. It was so fun meeting you.
- [19:20]
Norman
Send us your questions to vatrashbc.net au
- [19:24]
Tegan
and we'll catch you again next time.