Speaker 1: Hey, Welcome to Science Stuff, a production of iHeartRadio More. Hey,
Speaker 1: cham And today we're tackling the question what makes someone
Speaker 1: left handed? Is it something in your genes or is
Speaker 1: it random? And why do we involved to have a
Speaker 1: preference for one hand in the first place. We're going
Speaker 1: to talk to two scientists who have spent decades studying
Speaker 1: this phenomenon and who are going to step us through
Speaker 1: what it is, what causes it, and how to tell
Speaker 1: if you're actually left handed. It turns out you could
Speaker 1: have been wrong about it your whole life, So get
Speaker 1: ready to use both sides of your brain as we
Speaker 1: try to get a firm grasp on the right way
Speaker 1: to think about your left hand.
Speaker 2: Enjoy.
Speaker 1: Hey everyone. Today we're talking to two experts, each of
Speaker 1: whom have spent over twenty years studying left handedness. The
Speaker 1: first one is Professor Elka Kraus, and she has a
Speaker 1: very unique job when it comes to handed people. We'll
Speaker 1: talk about what that job is, but first I wanted
Speaker 1: to know what is the actual scientific definition of left handedness.
Speaker 1: As it turns out there is none, at least there's
Speaker 1: no definition scientists can agree on it. So here's my
Speaker 1: conversation with doctor Elka Krauss. Well, thank you doctor Kraus
Speaker 1: for joining us.
Speaker 3: Thank you.
Speaker 1: Can you please tell us who you are and what
Speaker 1: you do.
Speaker 3: I'm a professor for occupational therapy in Germany at University
Speaker 3: for Applied Sciences in Berlin, and one of my research
Speaker 3: topics is handedness. I've been studying it and researching it
Speaker 3: since the nineties.
Speaker 1: Amazing. Are you right handed or left handed?
Speaker 3: I'm right handed.
Speaker 1: Maybe to start us off, can you tell us what
Speaker 1: is handedness and how does it form in people?
Speaker 3: Yeah, so handedness is not just the hand that you
Speaker 3: write with us. Actually it's got two parts. It's the
Speaker 3: hand preference how often you use a hand, And it's
Speaker 3: the hand skill or proficiency, which is relative, so which
Speaker 3: hand is better than the other hand. They say that
Speaker 3: about between ten and twelve percent of humans are left
Speaker 3: handed and the rest is right handed. I see, But
Speaker 3: I just have to say that we have to look
Speaker 3: at that critically because defining handedness is very difficult. It's
Speaker 3: very complex. There's no standard definition of handedness. The way
Speaker 3: it's measured is very different. So some people only look
Speaker 3: at hand preference and the classification. When is a left
Speaker 3: hand or left handed is also not a standard. So
Speaker 3: these are the official numbers of ten to twelve percent
Speaker 3: left handedness, but I personally believe it could be a
Speaker 3: lot higher.
Speaker 1: Why is it difficult to measure handedness?
Speaker 3: Well, people have different ideas of what handedness is.
Speaker 1: I see, it's hard to measure because there's no consensus
Speaker 1: on how to measure it. Yes, so doctor Kraus is
Speaker 1: not your typical scientist. Her interest in what left handedness
Speaker 1: is comes from the very unique job that she has,
Speaker 1: which is to help little kids figure out if they
Speaker 1: are left handed or not. Well.
Speaker 3: The thing is, my context is that I work with
Speaker 3: children who are often on the verge, are going to
Speaker 3: school and who don't know which hand to write with,
Speaker 3: so they come to occupation as therapy to be assessed
Speaker 3: to see what hand should they write with. I see
Speaker 3: the problem is that if children learn to write with
Speaker 3: their non dominant hand, we call them switch handers. We
Speaker 3: know that they can have all sorts of problems because
Speaker 3: of that. They are consequences, and this makes handed there's
Speaker 3: not only a fascinating topic for me, but it actually
Speaker 3: is a very important one because occupation syrrapis in particular
Speaker 3: are co responsible for deciding which hand to write with.
Speaker 1: Okay, you might be thinking, here, it's not that hard
Speaker 1: to figure out which hand you should use to write with.
Speaker 1: You just give a kid a crayon or a pencil
Speaker 1: and see which hand they use. But as we'll talk
Speaker 1: about in a minute, for a lot of kids, it's
Speaker 1: not that simple, and the problem is that making the
Speaker 1: wrong choice can have pretty serious and life altering consequences. Okay,
Speaker 1: you mentioned that there are consequences for kids who are
Speaker 1: forced to use the hand that they're not handed with.
Speaker 3: So, as you might have heard, one hundred years ago,
Speaker 3: people were forced to be right handed, so left hand is.
Speaker 3: At school, they were taught to use the right hand,
Speaker 3: and if they didn't, that left hand was tied behind
Speaker 3: their back or they were actually hit on the hand.
Speaker 3: It was a very strong bias towards right handed, and
Speaker 3: as we speak, you could hear that language is also
Speaker 3: right biased, and so you are right, and it's got
Speaker 3: a bit of a negative thing in all sorts of languages.
Speaker 3: It goes back to a religious thing as well. One
Speaker 3: believe that the left side the devil was looking over
Speaker 3: your shoulder, so if you wrote with your left hand,
Speaker 3: the devil would be able to infuse these evil ideas
Speaker 3: into you. So you were doing the person a big
Speaker 3: favor by forcing them to write with the right hand.
Speaker 3: That caused a lot of painful a lot of left handers.
Speaker 3: Some then started to go back to write with their
Speaker 3: left hand at some point and they found that certain
Speaker 3: problems that they had concentration, memory, retention, also find motor
Speaker 3: coordination or gross motor coordination, you know, whatever they did
Speaker 3: actually became better, which just suddenly they could think free.
Speaker 3: So there's not that much good research on it, like
Speaker 3: control studies and whatever, but we have many sort of
Speaker 3: qualitative data on it. There's been some study on switch
Speaker 3: handers looking at the quality of life, and they did
Speaker 3: find that switch left handers feel that they have a
Speaker 3: lesser quality of life. They are motor proficiency problems, concentration
Speaker 3: learning problems, so they might actually have spelling difficulties, they
Speaker 3: might not remember things. They might be speech problems like
Speaker 3: stuttering going on, and and some moti visceral things like headaches, stomach,
Speaker 3: egche all of that. Because somehow writing, especially writing with
Speaker 3: a non dominant hand, seems to trigger all difficulties. So
Speaker 3: you can imagine if you had to do this, you
Speaker 3: would have to concentrate on so many other things to
Speaker 3: try and sort of get a reasonable result. It will
Speaker 3: never be as.
Speaker 1: Good right right. It'd be like living in a constant
Speaker 1: state of frustration and kind of constant state of feeling
Speaker 1: like there's obstacles. You're thinking, yeah, oh wow, I had
Speaker 1: never thought about how hard that must be. Absolutely, and
Speaker 1: that seems like a very big responsibility to kind of
Speaker 1: direct a kid to use a writer or left Yes,
Speaker 1: I know you might think it can't be that hard
Speaker 1: to tell if a kid is right or left handed,
Speaker 1: but here's the thing. We live in a right handed world.
Speaker 1: Doors are made to be used with your right hand, Toys,
Speaker 1: drinking cups, everything around us is mostly designed for right handers.
Speaker 1: And as a kid, you might see both your parents
Speaker 1: use their right hand to do things, and you might
Speaker 1: think that's the hand I should use. And so there
Speaker 1: are a lot of kids for whom it's not obvious
Speaker 1: whether they're right handed or left handed and which hand
Speaker 1: they should use to write with.
Speaker 3: If you're in a right handed world where everything is
Speaker 3: right hand orientated, then we cannot be sure that we
Speaker 3: just say let's let him write with the right hand,
Speaker 3: or let her write with the right hand because we
Speaker 3: might be switching somebody, usually a left handed So you
Speaker 3: can see that my point of departure is not just
Speaker 3: looking at handedness as a phenomenon, but it's actually identifying
Speaker 3: those children who might be left handers and preventing them
Speaker 3: from switching, or identifying switched handers and maybe reverting them
Speaker 3: back to their dominant hand.
Speaker 1: I see. Now, as doctor Krauss mentioned, there is no
Speaker 1: single definition of what left handedness is, but there are
Speaker 1: tends you can take that measure your handedness along several dimensions.
Speaker 3: So in my work, I've actually defined six dimensions off handedness.
Speaker 1: What are these six dimensions that you measure left handedness on?
Speaker 3: So, as I said the first two, the most important
Speaker 3: ones would be that you have preference and skill. You
Speaker 3: would think that would be the same thing, but it's
Speaker 3: not always that your preferred hand is also your better hand.
Speaker 1: Really, what, yes.
Speaker 3: Are you right handed or left handed?
Speaker 1: May I ask I'm right handed? Or wait? If you
Speaker 1: had to guess, would you be able to guess?
Speaker 3: No? But this is the thing. Right handed don't understand
Speaker 3: this necessary. They think that left handedness must be the
Speaker 3: opposite of right handedness. So anyway, Those are the two
Speaker 3: first dimensions. The second two are direction and then very
Speaker 3: importantly the extent of handedness. So you have hands, as
Speaker 3: I call them, that of verse very strongly handed. The
Speaker 3: right hander is that do everything right, left handed that
Speaker 3: do everything left. But that is actually the minority of people.
Speaker 3: Most people are moderately. The extent of hand is moderate.
Speaker 3: And then you have quite a big group in left
Speaker 3: handers that are very slightly left handed. They're not strongly
Speaker 3: left handed, that do a lot of things with the
Speaker 3: right hand really, and people don't understand that, and they
Speaker 3: called the mixed handers, but they're actually left handed. So
Speaker 3: there are some researchers that found that this group of
Speaker 3: left handers, they will always write with their left hand,
Speaker 3: but they might do more than half the things with
Speaker 3: the right hand.
Speaker 1: WHOA.
Speaker 3: We see this when we actually do differentiated assessments. So
Speaker 3: again there is this complex play or symphony of these
Speaker 3: different dimensions. Actually then determine which hand you use.
Speaker 1: WHOA. It's a lot more complicated than maye people think. Absolutely,
Speaker 1: it seems like you have these dimensions because some people
Speaker 1: might score high and based on one dimension, you might say, oh,
Speaker 1: this person's right handed, or left handed, but on another
Speaker 1: dimension it might be different. Yes, I see, And so
Speaker 1: what that tells you is that it's sort of a
Speaker 1: complicated thing and it's sort of on a spectrum. Is
Speaker 1: that kind of a big takeaway is that it's not
Speaker 1: just a right or left. There's sort of a lot
Speaker 1: of handedness in between. That's right.
Speaker 3: I think handedness is a continuum. So if you have
Speaker 3: extreme left, extreme right and somewhere you know, if every
Speaker 3: person is somewhere in between.
Speaker 1: Wow, But I guess we like binary things, so we
Speaker 1: might draw a line where it's right or left, but
Speaker 1: really it's a richer picture. Yes, people can have a
Speaker 1: preference for right left more or less, but it may
Speaker 1: not necessarily correlate to which hand is better at doing things.
Speaker 3: Yeah.
Speaker 1: Wow, I had to realize it's so complicated.
Speaker 3: Nor did I honestly when I started.
Speaker 1: Really wow, I have no idea all right. So there
Speaker 1: is no single definition of what left handedness is, and
Speaker 1: in fact, it seems to be on a spectrum. Some
Speaker 1: people are more left or right handed than others, And
Speaker 1: it's entirely possible that you could be a hidden left
Speaker 1: handed person and you only think you're right handed because
Speaker 1: that's what you were taught as a little kid. But
Speaker 1: here's the question, why are we handed in the first place?
Speaker 1: Why do we tend to have a preference, however strong
Speaker 1: it may be, to use one hand and not the other.
Speaker 1: Is it programmed in our genes? And why did we
Speaker 1: evolve this tendency to prefer one hand. When we come back,
Speaker 1: we're going to try our hand at answering these questions.
Speaker 1: So stay with us. We'll be right back. Hey, welcome back.
Speaker 1: We're talking about left handedness, and so far are we've
Speaker 1: talked about how hard it is to actually define it.
Speaker 1: Now we're going to talk about what actually causes it.
Speaker 1: Is it hereditary or random? Or are there other reasons
Speaker 1: why you choose to use one hand over the other.
Speaker 1: To help answer these questions, I reached out to another
Speaker 1: scientist who spent decades studying this phenomenon. Here's my conversation
Speaker 1: with doctor Sebastian Oglenburg. Well, thank you so much for
Speaker 1: joining us at you're Okenburg.
Speaker 4: Thank you so much for inviting me. I'm a germ
Speaker 4: professor of a research method in psychology at medical school
Speaker 4: in Hamburg and Northern Germany, and I spent the last
Speaker 4: twenty years doing research on left handedness and vainness symmetries.
Speaker 4: So I'm really interested in understanding why people are left
Speaker 4: tended and what it means to be left handed.
Speaker 1: Amazing that's perfect for us today.
Speaker 4: So left tendedness is, of course, on the surface, it's
Speaker 4: a preference in behavior, like people who are left tended
Speaker 4: like to use their left hand to do things like
Speaker 4: writing or drawing or using scissors. But handedness has nothing
Speaker 4: to do with the hands themselves, despite the name. If
Speaker 4: you ever looked at the hands the left hand and
Speaker 4: right hand, you would not be able to distinguish just
Speaker 4: by looking at the hand whose left handed, whose right
Speaker 4: handed right?
Speaker 2: So they're looking pretty identical.
Speaker 4: So handedness is something that has not much to do
Speaker 4: with the hands, but a lot to do with the brain.
Speaker 4: So what handedness is is a form of so called
Speaker 4: hemispheric asymmetries, meaning that our brain has two halves, and
Speaker 4: these two halves both do amazing things, but they do
Speaker 4: a little bit different things, and handedness is one form
Speaker 4: of these symmetries.
Speaker 1: Can you give us other examples of brain asymmetries.
Speaker 4: So these brain asymmetries are quite common, and there's a
Speaker 4: lot of things in a brain that are asymmetric. The
Speaker 4: most well known example language, so we know that for
Speaker 4: most people, language to speaking to other people and understanding
Speaker 4: what they're saying is controlled largely, not exclusively, by the
Speaker 4: left side of the brain. So for example, if you
Speaker 4: ever had a relative who suffered a stroke to the
Speaker 4: left side of the brain, they have severe problems with
Speaker 4: speaking in the weeks and months after they had the stroke.
Speaker 4: People who have a right sided stroke typically do not
Speaker 4: have this language problem. Other things that are quite come
Speaker 4: are the processing of faces. So for me, like to
Speaker 4: recognize your face, this is something that is mostly done
Speaker 4: by my right hemisphere, so it's a specific area called
Speaker 4: the fusiform face area that is located on the right
Speaker 4: side in most people, and so on. So there are
Speaker 4: many other things like visospatial attention, recognizing bodies of other people,
Speaker 4: mathematical operations, so a lot of things that are complicated
Speaker 4: and hard to do are organized in asymmetric networks, and
Speaker 4: handedness is one form of these the symmetry so it
Speaker 4: is a dominance of the motocortex, so the brain areas
Speaker 4: that are controlling our movements for things like writing, drawing,
Speaker 4: and so on. What we would call fine motor movements.
Speaker 4: So left handers have a right hemispheric motor dominance body
Speaker 4: sphinx and right handers a left hemispheric dominance because the
Speaker 4: left side of the brain is controlling the right side
Speaker 4: of the body and vice versa.
Speaker 1: WHOA, what does it mean dominant? It means it's better
Speaker 1: at things, or it it just kind of asserts control
Speaker 1: of things. What does dominant mean?
Speaker 2: It means several things.
Speaker 4: So for the one part, it means if you like
Speaker 4: decide consciously or subconsciously, like you want to draw a picture,
Speaker 4: then generally you would decide for your dominant hands. So
Speaker 4: on one part of it, it is a preference that
Speaker 4: you're having as a person. But this preference also goes
Speaker 4: along with differences in skill. So even if you would
Speaker 4: like draw with your nondamental left hand, you would not
Speaker 4: be able as much as you try to make the
Speaker 4: same quality of drawing, so there is a difference in skill.
Speaker 4: There's also neurobiological differences. So typically in a right hander,
Speaker 4: so the part of the motor cortex is representing the
Speaker 4: hand would be larger and have differential connections. So it's
Speaker 4: something that also develops over the course of your lifetime
Speaker 4: because your networks are not like completely fixed at birth.
Speaker 4: By you know, using your dominant hand more over your lifetime,
Speaker 4: you also strengthen connections to other networks in your brain.
Speaker 4: So it's the mixture of preference, skill, ill you're adda
Speaker 4: to me, and folastic training processes over the coursing f
Speaker 4: life time.
Speaker 1: Wow, that is very complicated. So handedness is a property
Speaker 1: of your brain, not your actual hands, and it has
Speaker 1: to do with the fact that your brain, for a
Speaker 1: lot of things, is a symmetrical It has two sides,
Speaker 1: and one side just happens to be more dominant for
Speaker 1: how you plan to move your body. For right handed people,
Speaker 1: it's the left side of your brain, and for left
Speaker 1: handed people it's the right side of the brain. Of course,
Speaker 1: Now the question is what causes one side of your
Speaker 1: brain to be more dominant and why is it that
Speaker 1: ninety percent of the time it ends up making people
Speaker 1: right handed versus ten percent of the time it makes
Speaker 1: them left handed. What causes left handedness? Like what causes
Speaker 1: for a right handed person, I need that left brain
Speaker 1: preference and skill and eventual training.
Speaker 4: So we know this is odso not as simple as
Speaker 4: people thought. So it is a trade that has substantial
Speaker 4: genetic contributions but also non genetic contributions. So there's a
Speaker 4: lot of exciting, large scale cooperative research that has shown
Speaker 4: that there's about forty eight locations in the genome that
Speaker 4: are relevant for handedness.
Speaker 2: You said, so it's forty eight.
Speaker 4: That the play roles quite interesting that the familial handedness
Speaker 4: has a strong effect on the child's handedness.
Speaker 2: With two left handed parents would.
Speaker 4: Get a child, the child as a much higher chance
Speaker 4: with also being left handed than the child of two
Speaker 4: right handed parents, And the same goes if there's just
Speaker 4: like one right handed one left handed parent, and the
Speaker 4: child would be intermediate.
Speaker 2: I see.
Speaker 1: Do we have a sense of what percentage left handedness
Speaker 1: is due to genetics?
Speaker 4: So we know from in studies and from other family
Speaker 4: studies it's probably around twenty five percent, which would mean
Speaker 4: there are seventy five percent of factors that are not
Speaker 4: directly explained by it. Wow, But it's also not generally
Speaker 4: very well understood whether remaining a seventy.
Speaker 2: Five percent come from I see.
Speaker 4: So they seem to be like sort of individual biological
Speaker 4: processes in a person that happens that might also be
Speaker 4: due to genetics, but are not caught very well, and
Speaker 4: these like twin family designed. So there's an ongoing discussion
Speaker 4: about this percentage because it seems to be quite low,
Speaker 4: so it might be higher.
Speaker 1: In fact, I see it might be higher than twenty
Speaker 1: five percent genetic, but not necessarily meaning the cost could
Speaker 1: be more genetic, but we don't know. Yes, yes, left
Speaker 1: handedness is not completely genetic. If both of your parents
Speaker 1: are left handed, then you do have a higher chance
Speaker 1: also being left handed, but it's not guaranteed. According to
Speaker 1: our experts, there's no one gene that makes you left handed.
Speaker 1: Scientists have found forty eight gens that seem to be involved,
Speaker 1: and they only predict about twenty five percent of left handedness.
Speaker 1: The rest could be things in your environment.
Speaker 4: There are also a couple of environmental, non genetic factors
Speaker 4: that play a role. For example, gender actually does so
Speaker 4: men are more likely to be left handed than women.
Speaker 4: There's also a couple other things, for example, people who
Speaker 4: have been like rest fed and for a higher chance
Speaker 4: of being right handed.
Speaker 1: Ah, so breastfeeding has something to do with it.
Speaker 4: Yeah, it's a very curious finding. So it seems to
Speaker 4: be a rather strong effect, which I don't think is
Speaker 4: well understood on a neurobiological level, but it seems to
Speaker 4: be there's an early effect of some sexophmoons on hand
Speaker 4: that's development of brainer symmetries.
Speaker 1: So the basic picture here is that handedness. Whether you
Speaker 1: prefer to use your right or left hand, but whether
Speaker 1: one hand is more skilled than the other, is all
Speaker 1: in your brain, and a lot can happen to your brain.
Speaker 1: Starting from the time you're growing inside your mother's womb
Speaker 1: as a fetus, your body basically has to start taking sides.
Speaker 1: For example, at some point yourselves have to decide which
Speaker 1: side of your body to grow the heart in. Yes,
Speaker 1: it's not a given that your heart will be on
Speaker 1: the left side of your chest. About one in twelve
Speaker 1: thousand babies conceived half dexterocardia, or the heart on the
Speaker 1: right side of the chest. There have even been cases
Speaker 1: of people finding out late in life that they have it.
Speaker 1: In twenty twenty three, who was reported in a medical
Speaker 1: journal that a perfectly healthy man one hundred and two
Speaker 1: years old went in for cataract surgery and during the
Speaker 1: checkup was stunned to find out his heart was on
Speaker 1: his right side. So you might want to double check
Speaker 1: that your heart is in the right place or the
Speaker 1: left place. I mean, but that's basically what happens with
Speaker 1: left handedness. According to doctor Okelenburg, when your fetus yourselves
Speaker 1: essentially start to pick which side of your brain will
Speaker 1: have the more dominant motor cortex. You can even start
Speaker 1: to see it and which hand the fetus uses.
Speaker 4: More So, if you look at altsound recordings of unborn fetuses,
Speaker 4: you could see that they already have some sort of preference.
Speaker 4: For example, they interact with their left or right hump
Speaker 4: a little bit more than by the other one. And
Speaker 4: if you then wait for the baby to be born
Speaker 4: and test them during school, then these like prenatal preferences
Speaker 4: forehand use predict the writing handedness with more than ninety
Speaker 4: five percent of curiosity.
Speaker 1: Now, scientists aren't really sure why your body picks one
Speaker 1: side or the other. It seems to be a combination
Speaker 1: of genes and hormones, and as we talked about before,
Speaker 1: this can also change after you're born, depending on what
Speaker 1: you're tagged as a kid. But here's the next big question,
Speaker 1: why even pick aside at all? What's the point of
Speaker 1: being handed? Why couldn't we all just be Ambidexter's or
Speaker 1: just as good with the left hand as the right hand.
Speaker 1: Why did humans evolve to have a hand preference? And
Speaker 1: are we the only animal in nature the ad has it.
Speaker 1: When we come back, I'll hand it over to our
Speaker 1: experts to answer these questions. So don't lose your grip
Speaker 1: on this podcast. We'll be right back. Hey, we'll come back.
Speaker 1: We're talking about left handedness with two scientists, and so
Speaker 1: far we've learned that the handedness sort of lies on
Speaker 1: a spectrum. Most people are strongly right hand and that
Speaker 1: a few people are strongly left handed, and some people
Speaker 1: are somewhere in between. We also learned scientists aren't sure
Speaker 1: what causes handedness. There are about forty eight genes associated
Speaker 1: with it, but how those genes affect which of your
Speaker 1: mortar cortex areas turns out to be the dominant one
Speaker 1: is still a mystery. And apparently these genes only account
Speaker 1: for about twenty five percent of whether you're right or
Speaker 1: left handed. The other seventy five percent could be environmental
Speaker 1: factors or hidden deeper in your genetic code. But now
Speaker 1: we're going to tackle an even bigger question, which is
Speaker 1: why are we handed in the first place, I mean,
Speaker 1: why pick aside, why aren't we all ambi dextrics. As
Speaker 1: it turns out, humans are not the only animal that
Speaker 1: takes up paw. You've written about the idea that there's
Speaker 1: handedness or potness in animals.
Speaker 2: Yeah, so in general, I've worked a lot on this.
Speaker 4: I think back in the day, people always thought did
Speaker 4: only humans show handedness? Because all humans right, But of
Speaker 4: course you cannot have a look at the writing patterns
Speaker 4: of a cat because they rarely use pets.
Speaker 2: But at some point people.
Speaker 4: Started to look at poor preferences or flipper preferences or
Speaker 4: whatever in animals, using experimental designs that would allow them
Speaker 4: to actually measure normal behavior.
Speaker 2: Of the animal.
Speaker 4: And what you find, Dan is that most animal species
Speaker 4: actually show left and right handedness. So asn enormous amount
Speaker 4: of studies on that. It's just just like more than
Speaker 4: one hundred different species it's been investigated, and I think
Speaker 4: the general pattern is that a lot of species show
Speaker 4: sort of like individual preferences.
Speaker 2: So if you.
Speaker 4: Look at a cat, most cats would have rather strong preference.
Speaker 2: For the right side or the left side.
Speaker 4: So what you could do, for example, if you have
Speaker 4: a cat at home, you want who knows the cat
Speaker 4: left port the right port. You could do something it's
Speaker 4: called the food reaching task. So you take like the
Speaker 4: little inlet from a toilet paper roll, close up one
Speaker 4: side with a little bit of like a cling wrap
Speaker 4: foil or whatever, and then you put like some like
Speaker 4: cat food tokens into this toilet paper roll and just
Speaker 4: have a look whether the cat is reaching into it
Speaker 4: with the left or the right paw. So if you
Speaker 4: use these kind of things, you typically find that individual
Speaker 4: cat has portaners. But in generally for a lot of
Speaker 4: animal species, left portners is more common than in humans.
Speaker 4: So we had this large meta analysis in twenty twenty
Speaker 4: about human handedness showing it's ten point six a percent
Speaker 4: of people are left handed, but if you look at
Speaker 4: cats or dogs, it's more like thirty to forty percent
Speaker 4: of animals being left pot So it seems to be
Speaker 4: animals do have handedness, but for a lot of animals species,
Speaker 4: left handedness left partners is much more common than in humans,
Speaker 4: so it goes more into like an equal distribution. There's
Speaker 4: also research with animals in the laboratory. So for example,
Speaker 4: people go to cat or dog hotels and ask the
Speaker 4: owners whether they can test their animals there while the
Speaker 4: owner's own vocation do a little bit of like interactions
Speaker 4: with them and then find out whether they're left or
Speaker 4: right port and be for example, also have some like
Speaker 4: citizen science projects where we ask people to record their
Speaker 4: animals with a smartphone while they are doing.
Speaker 2: Basically the scientific work.
Speaker 4: So there is a really big amount of research on
Speaker 4: animal hotness and handedness and generally shows humans are not
Speaker 4: unique or special in that.
Speaker 2: They have handedness. Most animal species have.
Speaker 1: It too, I see, but we're sort of unique in
Speaker 1: how much more prevalient right handedness is.
Speaker 2: Yeah, that's not completely unique.
Speaker 4: So there's also some parrot species to have about similar
Speaker 4: distributions of actually left.
Speaker 1: Clawdness really the way there are parents that skew the
Speaker 1: other way. They're like ninety percent left handed, left clawed.
Speaker 4: Yeah, left footed, claud whatever. There's a lot of research
Speaker 4: coming from Australia on that. So if you look at birds,
Speaker 4: a lot of birds don't do a lot of food
Speaker 4: handling with their claws, So parrots actually are species that
Speaker 4: do handle food and they also do other like a
Speaker 4: little bit more complicated tasks.
Speaker 1: Yes, it turns out humans are not the only animals
Speaker 1: with handedness or a side preference. Lots of animals have it,
Speaker 1: even down to flatworms which don't even have a brain.
Speaker 1: But that still doesn't answer the question of why this
Speaker 1: preference exists. Well, according to doctor Auglenburg, you might all
Speaker 1: have to do with efficient See.
Speaker 2: Why does this happen?
Speaker 4: I think this is sort of like a way of
Speaker 4: making our brains more efficient. Your brain is about two
Speaker 4: percent or so, depending a little bit of my over
Speaker 4: body weight, but it takes about twenty percent of all
Speaker 4: the calories I'm taking in to keeping it working. And
Speaker 4: so if you know the brain is the most energy
Speaker 4: hungry organ in the body, then it makes a lot
Speaker 4: of sense that you specialize that you have like networks
Speaker 4: that are only on one side, because if you double them,
Speaker 4: like for example, kidney or something, you would like increase
Speaker 4: the energy amount the organism needs without having like a
Speaker 4: direct gain in the situation. And the other thing is
Speaker 4: also if you do not take some like measures to
Speaker 4: make the brain efficient and as small as possible, at
Speaker 4: some point, umes would have been like really large heads,
Speaker 4: which would have all sorts of problems, for example, doing birth,
Speaker 4: doing like everyday life. You don't want to have a
Speaker 4: head like four times the size.
Speaker 1: Right, if we hadn't specialized the hemispheres, you mean.
Speaker 4: Yeah, So if you hadn't blessed the hemispheres and you
Speaker 4: would double everything in the brain, you would have had
Speaker 4: a much larger head. Right, So this would not be
Speaker 4: good for a number of reasons.
Speaker 1: All right, that makes sense. We didn't involve to be
Speaker 1: ambidexrous because for the most part, we don't really need
Speaker 1: two dexterus hands. It's more efficient to invest brain resources
Speaker 1: into making one of your hands more skilled than the other,
Speaker 1: because that's probably good enough for most tasks like using
Speaker 1: a tool or picking apart some food. But that still
Speaker 1: doesn't explain why humans are sort of unique having one
Speaker 1: kind of hand inness be more common than the other.
Speaker 1: As we mentioned before, most other animals have a nearly
Speaker 1: equal split between right and left handers or powers, but
Speaker 1: in humans, ninety percent of people are right handed. Why
Speaker 1: is that well? One idea, according totor Oglnburg, is that
Speaker 1: having most people need the same handed makes it easier
Speaker 1: to teach each other.
Speaker 4: And one of the ideas that it is just like
Speaker 4: easier to learn like a complicated thing if you.
Speaker 2: Don't have to like also mimor reverse it in your brain.
Speaker 4: Right, So if you're right handed, it's easier to learn
Speaker 4: writing from a right handed person because you can just
Speaker 4: like copy what.
Speaker 2: They're doing compared to a left handed person.
Speaker 4: So this ease of training and highly complicated things is
Speaker 4: something that is one of the hypothesis widest is such
Speaker 4: a strong right sided preference.
Speaker 1: I see and I read that there's something called the
Speaker 1: fighting hypothesis related to sort of the evolution of handedness.
Speaker 1: What does that mean?
Speaker 4: So there is a hypothesis that tries to link handedness
Speaker 4: directly to some sort of evolutionary survival fitness advantage. And
Speaker 4: the idea behind this is that left handers have a
Speaker 4: sort of like advantage in fighting in combat sports. It's
Speaker 4: very well known and there's a lot of research paper
Speaker 4: showing that. For example, I think like boxing, because a
Speaker 4: lot of people that do fight they've been trained in
Speaker 4: like fighting right handed opponents, which means that if you
Speaker 4: face the left handed opponents and they're attacking from basically
Speaker 4: the other side, you might have less experience in this
Speaker 4: sort of combat situation, and then the left tender might
Speaker 4: have a advantage. And this sort of like shows pretty
Speaker 4: well if you look at the sports for things like, oh,
Speaker 4: you call it like fencing. So the fighting advantage hypothesis
Speaker 4: is that left handers may stay in the population because
Speaker 4: they have a survival fitness advantage in fighting, but only
Speaker 4: as long as they're rare. If there's a lot of
Speaker 4: left handers there would be sort of like then destroying
Speaker 4: the advantage because then they're not very surprising anymore. Right, right,
Speaker 4: And it's a bit of an ongoing discussion whether you
Speaker 4: can explain behavior like directly with these fitness advantages, because
Speaker 4: I mean not sure how many fights you or your
Speaker 4: ancestors ever got that had direct relevance for your survial.
Speaker 4: So I would say it's a hypothesis. I would take
Speaker 4: it with a grain of salt.
Speaker 1: Okay, last question, anything else you think people should know
Speaker 1: about left handedness.
Speaker 4: I generally would say, your handedness is something that refers
Speaker 4: to the motor cortex. And if you look at like
Speaker 4: the largest meta studies integrating research over the last couple
Speaker 4: decades as pretty convincing evidence that left handedness and intelligence
Speaker 4: is not linked, so leatenders and right handers.
Speaker 2: Seem to be equally smart and capable.
Speaker 4: The same goes also for creativity, there was always this
Speaker 4: idea left handers some more creative, and it's.
Speaker 2: Quite interesting if you look at it.
Speaker 4: If you ask left and right handed people whether they
Speaker 4: believe left handers are more creative than right handers, is
Speaker 4: a ginormously strong statistical effect. So everybody believes left hand
Speaker 4: is some more creative than right handers.
Speaker 2: And actually parents use this that advice.
Speaker 4: Right, so you're really having a left handed child, you
Speaker 4: tell him become an.
Speaker 2: Artist or you become a rock star, whatever.
Speaker 4: But if you actually have left handers right handers create art,
Speaker 4: and then you take like artists who are experts in
Speaker 4: this field and let them rate the products, there's absolutely
Speaker 4: no difference. So I think in general you should think
Speaker 4: of handedness and something that is referring to the motorabilities.
Speaker 4: It's caused by the mortal cortex and does not have
Speaker 4: any sort of strong effect on like how smart you are, creative,
Speaker 4: you're any other like brain abilities, because it's just is
Speaker 4: not affecting the brain networks that do these things. Anything
Speaker 4: related to thinking or this idea there's sort of like
Speaker 4: a coherent left handed personality.
Speaker 2: They're rere spirited, creative thinkers and stuff like that.
Speaker 4: That's just very like old ideas that did not hold
Speaker 4: up very well.
Speaker 2: Sorry, left handers.
Speaker 1: So, left handers, is there anything else you think people
Speaker 1: should know about left handedness or handedness in general.
Speaker 3: Well, I think it's very important to look at left
Speaker 3: handedness as a normal form of handedness. There's nothing abnormal
Speaker 3: about it. They are just different in many ways.
Speaker 2: So this is.
Speaker 3: Really something that you cannot just change the handedness just
Speaker 3: by writing with that hand.
Speaker 1: I think you're saying that trying to switch someone doesn't
Speaker 1: just automatically flip the brain. It's like you're really forcing
Speaker 1: something that the brain is not predisposed to do.
Speaker 3: Yes, that's well said. You know that's not anything. So
Speaker 3: go to an occupation service, have been tested out and
Speaker 3: make sure that the child writes with the right hand.
Speaker 1: No, it was correct, yes, right, not the right hand,
Speaker 1: the correct hand. That's funny, all right. Well, it sounds
Speaker 1: like the question of why some people are left handed
Speaker 1: is still a bit of a mystery. We know a lot,
Speaker 1: but there's still a lot we don't know. I guess
Speaker 1: we just need to wait for the right person to
Speaker 1: figure out what's left. Hey, thanks for joining us. See
Speaker 1: you next time. You've been listening to Science Stuff production
Speaker 1: of iHeartRadio, written and produced by me or HM candidate
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