WEBVTT - What Makes Someone Left-Handed? 0:00:01.280 --> 0:00:04.960 Hey, Welcome to Science Stuff, a production of iHeartRadio More. Hey, 0:00:05.000 --> 0:00:08.160 cham And today we're tackling the question what makes someone 0:00:08.520 --> 0:00:12.320 left handed? Is it something in your genes or is 0:00:12.360 --> 0:00:15.160 it random? And why do we involved to have a 0:00:15.240 --> 0:00:18.520 preference for one hand in the first place. We're going 0:00:18.560 --> 0:00:21.240 to talk to two scientists who have spent decades studying 0:00:21.280 --> 0:00:23.799 this phenomenon and who are going to step us through 0:00:24.000 --> 0:00:27.160 what it is, what causes it, and how to tell 0:00:27.240 --> 0:00:30.480 if you're actually left handed. It turns out you could 0:00:30.480 --> 0:00:35.839 have been wrong about it your whole life, So get 0:00:35.920 --> 0:00:38.239 ready to use both sides of your brain as we 0:00:38.280 --> 0:00:41.040 try to get a firm grasp on the right way 0:00:41.080 --> 0:00:43.120 to think about your left hand. 0:00:43.920 --> 0:00:44.240 Enjoy. 0:00:46.720 --> 0:00:49.960 Hey everyone. Today we're talking to two experts, each of 0:00:50.000 --> 0:00:54.320 whom have spent over twenty years studying left handedness. The 0:00:54.360 --> 0:00:57.560 first one is Professor Elka Kraus, and she has a 0:00:57.760 --> 0:01:01.440 very unique job when it comes to handed people. We'll 0:01:01.440 --> 0:01:04.080 talk about what that job is, but first I wanted 0:01:04.080 --> 0:01:08.679 to know what is the actual scientific definition of left handedness. 0:01:08.920 --> 0:01:11.920 As it turns out there is none, at least there's 0:01:11.959 --> 0:01:15.360 no definition scientists can agree on it. So here's my 0:01:15.400 --> 0:01:20.360 conversation with doctor Elka Krauss. Well, thank you doctor Kraus 0:01:20.360 --> 0:01:21.000 for joining us. 0:01:21.240 --> 0:01:21.720 Thank you. 0:01:21.760 --> 0:01:23.120 Can you please tell us who you are and what 0:01:23.200 --> 0:01:23.399 you do. 0:01:24.000 --> 0:01:28.000 I'm a professor for occupational therapy in Germany at University 0:01:28.080 --> 0:01:31.720 for Applied Sciences in Berlin, and one of my research 0:01:31.840 --> 0:01:36.880 topics is handedness. I've been studying it and researching it 0:01:37.040 --> 0:01:38.319 since the nineties. 0:01:38.640 --> 0:01:41.039 Amazing. Are you right handed or left handed? 0:01:41.160 --> 0:01:41.919 I'm right handed. 0:01:42.080 --> 0:01:44.280 Maybe to start us off, can you tell us what 0:01:44.440 --> 0:01:47.160 is handedness and how does it form in people? 0:01:47.360 --> 0:01:50.840 Yeah, so handedness is not just the hand that you 0:01:50.960 --> 0:01:53.360 write with us. Actually it's got two parts. It's the 0:01:53.440 --> 0:01:57.000 hand preference how often you use a hand, And it's 0:01:57.040 --> 0:02:00.520 the hand skill or proficiency, which is relative, so which 0:02:00.560 --> 0:02:03.480 hand is better than the other hand. They say that 0:02:03.520 --> 0:02:07.240 about between ten and twelve percent of humans are left 0:02:07.280 --> 0:02:09.960 handed and the rest is right handed. I see, But 0:02:10.280 --> 0:02:12.600 I just have to say that we have to look 0:02:12.600 --> 0:02:16.040 at that critically because defining handedness is very difficult. It's 0:02:16.160 --> 0:02:20.120 very complex. There's no standard definition of handedness. The way 0:02:20.160 --> 0:02:23.079 it's measured is very different. So some people only look 0:02:23.160 --> 0:02:26.959 at hand preference and the classification. When is a left 0:02:26.960 --> 0:02:29.960 hand or left handed is also not a standard. So 0:02:30.240 --> 0:02:33.720 these are the official numbers of ten to twelve percent 0:02:33.840 --> 0:02:37.640 left handedness, but I personally believe it could be a 0:02:37.639 --> 0:02:38.320 lot higher. 0:02:38.840 --> 0:02:41.160 Why is it difficult to measure handedness? 0:02:41.400 --> 0:02:44.400 Well, people have different ideas of what handedness is. 0:02:44.560 --> 0:02:47.600 I see, it's hard to measure because there's no consensus 0:02:47.600 --> 0:02:51.000 on how to measure it. Yes, so doctor Kraus is 0:02:51.000 --> 0:02:54.760 not your typical scientist. Her interest in what left handedness 0:02:54.880 --> 0:02:57.720 is comes from the very unique job that she has, 0:02:58.040 --> 0:03:01.240 which is to help little kids figure out if they 0:03:01.240 --> 0:03:04.680 are left handed or not. Well. 0:03:04.919 --> 0:03:06.880 The thing is, my context is that I work with 0:03:07.040 --> 0:03:10.120 children who are often on the verge, are going to 0:03:10.160 --> 0:03:12.120 school and who don't know which hand to write with, 0:03:12.520 --> 0:03:16.280 so they come to occupation as therapy to be assessed 0:03:16.440 --> 0:03:19.320 to see what hand should they write with. I see 0:03:19.639 --> 0:03:22.760 the problem is that if children learn to write with 0:03:22.919 --> 0:03:26.600 their non dominant hand, we call them switch handers. We 0:03:26.760 --> 0:03:29.280 know that they can have all sorts of problems because 0:03:29.320 --> 0:03:33.119 of that. They are consequences, and this makes handed there's 0:03:33.160 --> 0:03:36.280 not only a fascinating topic for me, but it actually 0:03:36.520 --> 0:03:40.520 is a very important one because occupation syrrapis in particular 0:03:40.800 --> 0:03:43.960 are co responsible for deciding which hand to write with. 0:03:45.240 --> 0:03:47.560 Okay, you might be thinking, here, it's not that hard 0:03:47.560 --> 0:03:50.080 to figure out which hand you should use to write with. 0:03:50.360 --> 0:03:52.760 You just give a kid a crayon or a pencil 0:03:53.040 --> 0:03:55.840 and see which hand they use. But as we'll talk 0:03:55.840 --> 0:03:58.280 about in a minute, for a lot of kids, it's 0:03:58.400 --> 0:04:01.120 not that simple, and the problem is that making the 0:04:01.160 --> 0:04:08.000 wrong choice can have pretty serious and life altering consequences. Okay, 0:04:08.120 --> 0:04:11.560 you mentioned that there are consequences for kids who are 0:04:11.600 --> 0:04:13.920 forced to use the hand that they're not handed with. 0:04:14.400 --> 0:04:17.360 So, as you might have heard, one hundred years ago, 0:04:17.480 --> 0:04:19.960 people were forced to be right handed, so left hand is. 0:04:20.040 --> 0:04:23.080 At school, they were taught to use the right hand, 0:04:23.120 --> 0:04:25.560 and if they didn't, that left hand was tied behind 0:04:25.560 --> 0:04:28.520 their back or they were actually hit on the hand. 0:04:28.760 --> 0:04:31.839 It was a very strong bias towards right handed, and 0:04:31.920 --> 0:04:34.600 as we speak, you could hear that language is also 0:04:34.760 --> 0:04:39.080 right biased, and so you are right, and it's got 0:04:39.080 --> 0:04:42.320 a bit of a negative thing in all sorts of languages. 0:04:42.440 --> 0:04:45.159 It goes back to a religious thing as well. One 0:04:45.200 --> 0:04:48.159 believe that the left side the devil was looking over 0:04:48.200 --> 0:04:50.200 your shoulder, so if you wrote with your left hand, 0:04:50.560 --> 0:04:55.520 the devil would be able to infuse these evil ideas 0:04:55.560 --> 0:04:58.240 into you. So you were doing the person a big 0:04:58.279 --> 0:05:01.240 favor by forcing them to write with the right hand. 0:05:02.040 --> 0:05:05.120 That caused a lot of painful a lot of left handers. 0:05:05.160 --> 0:05:08.240 Some then started to go back to write with their 0:05:08.320 --> 0:05:12.240 left hand at some point and they found that certain 0:05:12.279 --> 0:05:17.840 problems that they had concentration, memory, retention, also find motor 0:05:17.920 --> 0:05:21.520 coordination or gross motor coordination, you know, whatever they did 0:05:21.640 --> 0:05:26.240 actually became better, which just suddenly they could think free. 0:05:27.440 --> 0:05:30.479 So there's not that much good research on it, like 0:05:30.560 --> 0:05:33.440 control studies and whatever, but we have many sort of 0:05:33.520 --> 0:05:37.080 qualitative data on it. There's been some study on switch 0:05:37.160 --> 0:05:40.440 handers looking at the quality of life, and they did 0:05:40.600 --> 0:05:43.960 find that switch left handers feel that they have a 0:05:44.080 --> 0:05:49.720 lesser quality of life. They are motor proficiency problems, concentration 0:05:49.960 --> 0:05:53.800 learning problems, so they might actually have spelling difficulties, they 0:05:53.880 --> 0:05:56.919 might not remember things. They might be speech problems like 0:05:57.040 --> 0:06:03.760 stuttering going on, and and some moti visceral things like headaches, stomach, 0:06:03.839 --> 0:06:08.120 egche all of that. Because somehow writing, especially writing with 0:06:08.200 --> 0:06:11.919 a non dominant hand, seems to trigger all difficulties. So 0:06:12.000 --> 0:06:13.960 you can imagine if you had to do this, you 0:06:14.000 --> 0:06:16.479 would have to concentrate on so many other things to 0:06:16.600 --> 0:06:19.680 try and sort of get a reasonable result. It will 0:06:19.720 --> 0:06:20.640 never be as. 0:06:20.480 --> 0:06:23.560 Good right right. It'd be like living in a constant 0:06:23.600 --> 0:06:28.840 state of frustration and kind of constant state of feeling 0:06:28.880 --> 0:06:32.600 like there's obstacles. You're thinking, yeah, oh wow, I had 0:06:32.640 --> 0:06:36.360 never thought about how hard that must be. Absolutely, and 0:06:36.480 --> 0:06:39.800 that seems like a very big responsibility to kind of 0:06:39.920 --> 0:06:42.880 direct a kid to use a writer or left Yes, 0:06:44.040 --> 0:06:46.240 I know you might think it can't be that hard 0:06:46.279 --> 0:06:48.320 to tell if a kid is right or left handed, 0:06:48.720 --> 0:06:52.840 but here's the thing. We live in a right handed world. 0:06:53.160 --> 0:06:57.320 Doors are made to be used with your right hand, Toys, 0:06:57.440 --> 0:07:02.839 drinking cups, everything around us is mostly designed for right handers. 0:07:03.200 --> 0:07:05.640 And as a kid, you might see both your parents 0:07:05.760 --> 0:07:07.920 use their right hand to do things, and you might 0:07:07.960 --> 0:07:10.600 think that's the hand I should use. And so there 0:07:10.600 --> 0:07:13.080 are a lot of kids for whom it's not obvious 0:07:13.160 --> 0:07:16.240 whether they're right handed or left handed and which hand 0:07:16.320 --> 0:07:17.600 they should use to write with. 0:07:19.160 --> 0:07:21.480 If you're in a right handed world where everything is 0:07:21.560 --> 0:07:25.440 right hand orientated, then we cannot be sure that we 0:07:25.680 --> 0:07:28.120 just say let's let him write with the right hand, 0:07:28.480 --> 0:07:30.200 or let her write with the right hand because we 0:07:30.280 --> 0:07:34.000 might be switching somebody, usually a left handed So you 0:07:34.040 --> 0:07:37.520 can see that my point of departure is not just 0:07:37.840 --> 0:07:42.200 looking at handedness as a phenomenon, but it's actually identifying 0:07:42.280 --> 0:07:45.840 those children who might be left handers and preventing them 0:07:45.840 --> 0:07:50.760 from switching, or identifying switched handers and maybe reverting them 0:07:50.800 --> 0:07:52.559 back to their dominant hand. 0:07:52.840 --> 0:07:56.600 I see. Now, as doctor Krauss mentioned, there is no 0:07:56.840 --> 0:08:01.120 single definition of what left handedness is, but there are 0:08:01.240 --> 0:08:06.640 tends you can take that measure your handedness along several dimensions. 0:08:08.480 --> 0:08:12.720 So in my work, I've actually defined six dimensions off handedness. 0:08:12.760 --> 0:08:15.920 What are these six dimensions that you measure left handedness on? 0:08:16.400 --> 0:08:19.520 So, as I said the first two, the most important 0:08:19.640 --> 0:08:23.400 ones would be that you have preference and skill. You 0:08:23.440 --> 0:08:26.000 would think that would be the same thing, but it's 0:08:26.080 --> 0:08:28.720 not always that your preferred hand is also your better hand. 0:08:29.280 --> 0:08:32.120 Really, what, yes. 0:08:31.920 --> 0:08:33.319 Are you right handed or left handed? 0:08:33.360 --> 0:08:35.960 May I ask I'm right handed? Or wait? If you 0:08:35.960 --> 0:08:37.679 had to guess, would you be able to guess? 0:08:37.920 --> 0:08:43.720 No? But this is the thing. Right handed don't understand 0:08:43.720 --> 0:08:47.000 this necessary. They think that left handedness must be the 0:08:47.000 --> 0:08:49.760 opposite of right handedness. So anyway, Those are the two 0:08:49.800 --> 0:08:54.079 first dimensions. The second two are direction and then very 0:08:54.120 --> 0:08:58.360 importantly the extent of handedness. So you have hands, as 0:08:58.400 --> 0:09:01.520 I call them, that of verse very strongly handed. The 0:09:01.600 --> 0:09:03.679 right hander is that do everything right, left handed that 0:09:03.760 --> 0:09:07.080 do everything left. But that is actually the minority of people. 0:09:07.600 --> 0:09:11.520 Most people are moderately. The extent of hand is moderate. 0:09:11.679 --> 0:09:14.079 And then you have quite a big group in left 0:09:14.080 --> 0:09:18.160 handers that are very slightly left handed. They're not strongly 0:09:18.240 --> 0:09:20.080 left handed, that do a lot of things with the 0:09:20.160 --> 0:09:23.560 right hand really, and people don't understand that, and they 0:09:23.679 --> 0:09:26.320 called the mixed handers, but they're actually left handed. So 0:09:26.480 --> 0:09:28.560 there are some researchers that found that this group of 0:09:28.640 --> 0:09:30.800 left handers, they will always write with their left hand, 0:09:31.120 --> 0:09:33.760 but they might do more than half the things with 0:09:33.840 --> 0:09:34.440 the right hand. 0:09:34.520 --> 0:09:35.400 WHOA. 0:09:36.559 --> 0:09:40.280 We see this when we actually do differentiated assessments. So 0:09:40.360 --> 0:09:44.839 again there is this complex play or symphony of these 0:09:44.840 --> 0:09:48.520 different dimensions. Actually then determine which hand you use. 0:09:49.040 --> 0:09:53.880 WHOA. It's a lot more complicated than maye people think. Absolutely, 0:09:56.000 --> 0:09:59.280 it seems like you have these dimensions because some people 0:09:59.360 --> 0:10:02.040 might score high and based on one dimension, you might say, oh, 0:10:02.120 --> 0:10:04.320 this person's right handed, or left handed, but on another 0:10:04.360 --> 0:10:08.800 dimension it might be different. Yes, I see, And so 0:10:08.960 --> 0:10:10.680 what that tells you is that it's sort of a 0:10:10.760 --> 0:10:13.760 complicated thing and it's sort of on a spectrum. Is 0:10:13.760 --> 0:10:16.480 that kind of a big takeaway is that it's not 0:10:16.600 --> 0:10:19.319 just a right or left. There's sort of a lot 0:10:19.360 --> 0:10:21.800 of handedness in between. That's right. 0:10:22.080 --> 0:10:25.320 I think handedness is a continuum. So if you have 0:10:25.559 --> 0:10:29.520 extreme left, extreme right and somewhere you know, if every 0:10:29.559 --> 0:10:31.560 person is somewhere in between. 0:10:31.760 --> 0:10:34.960 Wow, But I guess we like binary things, so we 0:10:35.080 --> 0:10:37.920 might draw a line where it's right or left, but 0:10:38.000 --> 0:10:41.320 really it's a richer picture. Yes, people can have a 0:10:41.400 --> 0:10:45.439 preference for right left more or less, but it may 0:10:45.480 --> 0:10:48.760 not necessarily correlate to which hand is better at doing things. 0:10:49.080 --> 0:10:49.520 Yeah. 0:10:49.559 --> 0:10:52.760 Wow, I had to realize it's so complicated. 0:10:52.240 --> 0:10:54.280 Nor did I honestly when I started. 0:10:54.840 --> 0:10:59.640 Really wow, I have no idea all right. So there 0:10:59.679 --> 0:11:03.400 is no single definition of what left handedness is, and 0:11:03.679 --> 0:11:06.520 in fact, it seems to be on a spectrum. Some 0:11:06.559 --> 0:11:09.520 people are more left or right handed than others, And 0:11:09.640 --> 0:11:13.200 it's entirely possible that you could be a hidden left 0:11:13.200 --> 0:11:16.439 handed person and you only think you're right handed because 0:11:16.600 --> 0:11:19.240 that's what you were taught as a little kid. But 0:11:19.280 --> 0:11:22.559 here's the question, why are we handed in the first place? 0:11:23.000 --> 0:11:25.640 Why do we tend to have a preference, however strong 0:11:25.679 --> 0:11:28.880 it may be, to use one hand and not the other. 0:11:29.440 --> 0:11:32.120 Is it programmed in our genes? And why did we 0:11:32.200 --> 0:11:36.560 evolve this tendency to prefer one hand. When we come back, 0:11:36.800 --> 0:11:39.640 we're going to try our hand at answering these questions. 0:11:40.040 --> 0:11:56.600 So stay with us. We'll be right back. Hey, welcome back. 0:11:57.040 --> 0:12:00.400 We're talking about left handedness, and so far are we've 0:12:00.440 --> 0:12:03.360 talked about how hard it is to actually define it. 0:12:03.760 --> 0:12:06.840 Now we're going to talk about what actually causes it. 0:12:06.880 --> 0:12:10.760 Is it hereditary or random? Or are there other reasons 0:12:10.840 --> 0:12:13.520 why you choose to use one hand over the other. 0:12:14.040 --> 0:12:16.520 To help answer these questions, I reached out to another 0:12:16.600 --> 0:12:21.120 scientist who spent decades studying this phenomenon. Here's my conversation 0:12:21.200 --> 0:12:25.200 with doctor Sebastian Oglenburg. Well, thank you so much for 0:12:25.280 --> 0:12:26.599 joining us at you're Okenburg. 0:12:26.880 --> 0:12:29.920 Thank you so much for inviting me. I'm a germ 0:12:30.000 --> 0:12:34.400 professor of a research method in psychology at medical school 0:12:34.840 --> 0:12:38.440 in Hamburg and Northern Germany, and I spent the last 0:12:38.480 --> 0:12:42.960 twenty years doing research on left handedness and vainness symmetries. 0:12:43.320 --> 0:12:47.280 So I'm really interested in understanding why people are left 0:12:47.320 --> 0:12:49.480 tended and what it means to be left handed. 0:12:49.679 --> 0:12:51.600 Amazing that's perfect for us today. 0:12:52.360 --> 0:12:56.040 So left tendedness is, of course, on the surface, it's 0:12:56.120 --> 0:12:59.920 a preference in behavior, like people who are left tended 0:13:00.160 --> 0:13:02.520 like to use their left hand to do things like 0:13:02.760 --> 0:13:07.360 writing or drawing or using scissors. But handedness has nothing 0:13:07.440 --> 0:13:11.199 to do with the hands themselves, despite the name. If 0:13:11.200 --> 0:13:14.439 you ever looked at the hands the left hand and 0:13:14.559 --> 0:13:17.600 right hand, you would not be able to distinguish just 0:13:17.960 --> 0:13:20.840 by looking at the hand whose left handed, whose right 0:13:20.880 --> 0:13:21.440 handed right? 0:13:21.480 --> 0:13:23.400 So they're looking pretty identical. 0:13:23.640 --> 0:13:27.360 So handedness is something that has not much to do 0:13:27.400 --> 0:13:30.920 with the hands, but a lot to do with the brain. 0:13:31.440 --> 0:13:35.200 So what handedness is is a form of so called 0:13:35.240 --> 0:13:40.280 hemispheric asymmetries, meaning that our brain has two halves, and 0:13:40.400 --> 0:13:43.840 these two halves both do amazing things, but they do 0:13:43.920 --> 0:13:47.720 a little bit different things, and handedness is one form 0:13:47.800 --> 0:13:48.920 of these symmetries. 0:13:49.480 --> 0:13:51.920 Can you give us other examples of brain asymmetries. 0:13:52.400 --> 0:13:55.600 So these brain asymmetries are quite common, and there's a 0:13:55.679 --> 0:13:58.520 lot of things in a brain that are asymmetric. The 0:13:58.559 --> 0:14:02.000 most well known example language, so we know that for 0:14:02.160 --> 0:14:07.080 most people, language to speaking to other people and understanding 0:14:07.080 --> 0:14:12.360 what they're saying is controlled largely, not exclusively, by the 0:14:12.440 --> 0:14:15.040 left side of the brain. So for example, if you 0:14:15.320 --> 0:14:19.400 ever had a relative who suffered a stroke to the 0:14:19.520 --> 0:14:23.960 left side of the brain, they have severe problems with 0:14:24.080 --> 0:14:27.480 speaking in the weeks and months after they had the stroke. 0:14:27.800 --> 0:14:31.840 People who have a right sided stroke typically do not 0:14:31.920 --> 0:14:36.240 have this language problem. Other things that are quite come 0:14:36.560 --> 0:14:40.600 are the processing of faces. So for me, like to 0:14:40.760 --> 0:14:44.800 recognize your face, this is something that is mostly done 0:14:45.000 --> 0:14:48.920 by my right hemisphere, so it's a specific area called 0:14:48.920 --> 0:14:53.040 the fusiform face area that is located on the right 0:14:53.120 --> 0:14:56.160 side in most people, and so on. So there are 0:14:56.160 --> 0:15:01.480 many other things like visospatial attention, recognizing bodies of other people, 0:15:01.640 --> 0:15:06.160 mathematical operations, so a lot of things that are complicated 0:15:06.240 --> 0:15:10.920 and hard to do are organized in asymmetric networks, and 0:15:11.000 --> 0:15:14.200 handedness is one form of these the symmetry so it 0:15:14.240 --> 0:15:19.280 is a dominance of the motocortex, so the brain areas 0:15:19.320 --> 0:15:23.600 that are controlling our movements for things like writing, drawing, 0:15:23.720 --> 0:15:26.600 and so on. What we would call fine motor movements. 0:15:27.240 --> 0:15:31.880 So left handers have a right hemispheric motor dominance body 0:15:31.880 --> 0:15:36.520 sphinx and right handers a left hemispheric dominance because the 0:15:36.640 --> 0:15:39.520 left side of the brain is controlling the right side 0:15:39.560 --> 0:15:41.320 of the body and vice versa. 0:15:42.480 --> 0:15:45.120 WHOA, what does it mean dominant? It means it's better 0:15:45.160 --> 0:15:48.760 at things, or it it just kind of asserts control 0:15:48.840 --> 0:15:50.320 of things. What does dominant mean? 0:15:50.720 --> 0:15:52.320 It means several things. 0:15:52.360 --> 0:15:55.320 So for the one part, it means if you like 0:15:55.680 --> 0:15:59.800 decide consciously or subconsciously, like you want to draw a picture, 0:16:00.160 --> 0:16:04.880 then generally you would decide for your dominant hands. So 0:16:04.960 --> 0:16:07.960 on one part of it, it is a preference that 0:16:08.040 --> 0:16:11.680 you're having as a person. But this preference also goes 0:16:11.800 --> 0:16:15.600 along with differences in skill. So even if you would 0:16:15.640 --> 0:16:18.880 like draw with your nondamental left hand, you would not 0:16:19.000 --> 0:16:21.920 be able as much as you try to make the 0:16:22.000 --> 0:16:26.280 same quality of drawing, so there is a difference in skill. 0:16:27.200 --> 0:16:32.040 There's also neurobiological differences. So typically in a right hander, 0:16:32.240 --> 0:16:35.160 so the part of the motor cortex is representing the 0:16:35.280 --> 0:16:39.840 hand would be larger and have differential connections. So it's 0:16:39.840 --> 0:16:43.960 something that also develops over the course of your lifetime 0:16:44.040 --> 0:16:48.520 because your networks are not like completely fixed at birth. 0:16:49.040 --> 0:16:52.720 By you know, using your dominant hand more over your lifetime, 0:16:52.800 --> 0:16:56.640 you also strengthen connections to other networks in your brain. 0:16:57.160 --> 0:17:01.280 So it's the mixture of preference, skill, ill you're adda 0:17:01.400 --> 0:17:06.119 to me, and folastic training processes over the coursing f 0:17:06.119 --> 0:17:06.520 life time. 0:17:06.600 --> 0:17:12.600 Wow, that is very complicated. So handedness is a property 0:17:12.640 --> 0:17:16.120 of your brain, not your actual hands, and it has 0:17:16.160 --> 0:17:18.280 to do with the fact that your brain, for a 0:17:18.320 --> 0:17:22.240 lot of things, is a symmetrical It has two sides, 0:17:22.280 --> 0:17:25.280 and one side just happens to be more dominant for 0:17:25.359 --> 0:17:28.359 how you plan to move your body. For right handed people, 0:17:28.400 --> 0:17:30.720 it's the left side of your brain, and for left 0:17:30.720 --> 0:17:34.080 handed people it's the right side of the brain. Of course, 0:17:34.200 --> 0:17:36.800 Now the question is what causes one side of your 0:17:36.840 --> 0:17:39.520 brain to be more dominant and why is it that 0:17:39.600 --> 0:17:42.000 ninety percent of the time it ends up making people 0:17:42.200 --> 0:17:45.080 right handed versus ten percent of the time it makes 0:17:45.119 --> 0:17:51.640 them left handed. What causes left handedness? Like what causes 0:17:52.400 --> 0:17:55.280 for a right handed person, I need that left brain 0:17:55.920 --> 0:17:59.000 preference and skill and eventual training. 0:17:59.320 --> 0:18:02.640 So we know this is odso not as simple as 0:18:02.800 --> 0:18:08.480 people thought. So it is a trade that has substantial 0:18:08.680 --> 0:18:13.560 genetic contributions but also non genetic contributions. So there's a 0:18:13.600 --> 0:18:19.159 lot of exciting, large scale cooperative research that has shown 0:18:19.280 --> 0:18:24.199 that there's about forty eight locations in the genome that 0:18:24.320 --> 0:18:25.840 are relevant for handedness. 0:18:26.000 --> 0:18:28.960 You said, so it's forty eight. 0:18:29.040 --> 0:18:34.240 That the play roles quite interesting that the familial handedness 0:18:34.440 --> 0:18:36.879 has a strong effect on the child's handedness. 0:18:36.920 --> 0:18:39.360 With two left handed parents would. 0:18:39.280 --> 0:18:41.760 Get a child, the child as a much higher chance 0:18:41.800 --> 0:18:44.320 with also being left handed than the child of two 0:18:44.520 --> 0:18:47.439 right handed parents, And the same goes if there's just 0:18:47.560 --> 0:18:50.719 like one right handed one left handed parent, and the 0:18:50.840 --> 0:18:52.160 child would be intermediate. 0:18:53.560 --> 0:18:53.960 I see. 0:18:53.960 --> 0:18:56.840 Do we have a sense of what percentage left handedness 0:18:57.000 --> 0:18:58.280 is due to genetics? 0:18:58.359 --> 0:19:03.160 So we know from in studies and from other family 0:19:03.280 --> 0:19:07.640 studies it's probably around twenty five percent, which would mean 0:19:07.680 --> 0:19:10.720 there are seventy five percent of factors that are not 0:19:10.840 --> 0:19:14.400 directly explained by it. Wow, But it's also not generally 0:19:14.560 --> 0:19:17.960 very well understood whether remaining a seventy. 0:19:17.600 --> 0:19:20.000 Five percent come from I see. 0:19:20.160 --> 0:19:24.560 So they seem to be like sort of individual biological 0:19:24.880 --> 0:19:28.399 processes in a person that happens that might also be 0:19:28.560 --> 0:19:31.359 due to genetics, but are not caught very well, and 0:19:31.440 --> 0:19:36.520 these like twin family designed. So there's an ongoing discussion 0:19:36.880 --> 0:19:40.359 about this percentage because it seems to be quite low, 0:19:40.800 --> 0:19:41.640 so it might be higher. 0:19:41.720 --> 0:19:44.760 In fact, I see it might be higher than twenty 0:19:44.760 --> 0:19:48.200 five percent genetic, but not necessarily meaning the cost could 0:19:48.240 --> 0:19:53.440 be more genetic, but we don't know. Yes, yes, left 0:19:53.440 --> 0:19:57.320 handedness is not completely genetic. If both of your parents 0:19:57.359 --> 0:19:59.960 are left handed, then you do have a higher chance 0:20:00.240 --> 0:20:04.240 also being left handed, but it's not guaranteed. According to 0:20:04.240 --> 0:20:08.080 our experts, there's no one gene that makes you left handed. 0:20:08.440 --> 0:20:11.880 Scientists have found forty eight gens that seem to be involved, 0:20:12.119 --> 0:20:16.280 and they only predict about twenty five percent of left handedness. 0:20:16.640 --> 0:20:19.080 The rest could be things in your environment. 0:20:20.000 --> 0:20:23.960 There are also a couple of environmental, non genetic factors 0:20:24.000 --> 0:20:27.760 that play a role. For example, gender actually does so 0:20:27.920 --> 0:20:31.760 men are more likely to be left handed than women. 0:20:32.560 --> 0:20:36.640 There's also a couple other things, for example, people who 0:20:36.680 --> 0:20:39.840 have been like rest fed and for a higher chance 0:20:40.000 --> 0:20:41.040 of being right handed. 0:20:41.280 --> 0:20:44.720 Ah, so breastfeeding has something to do with it. 0:20:45.160 --> 0:20:47.600 Yeah, it's a very curious finding. So it seems to 0:20:47.640 --> 0:20:51.359 be a rather strong effect, which I don't think is 0:20:51.440 --> 0:20:55.879 well understood on a neurobiological level, but it seems to 0:20:55.920 --> 0:20:59.840 be there's an early effect of some sexophmoons on hand 0:21:00.160 --> 0:21:02.800 that's development of brainer symmetries. 0:21:03.880 --> 0:21:06.920 So the basic picture here is that handedness. Whether you 0:21:07.000 --> 0:21:09.520 prefer to use your right or left hand, but whether 0:21:09.560 --> 0:21:12.640 one hand is more skilled than the other, is all 0:21:12.640 --> 0:21:15.439 in your brain, and a lot can happen to your brain. 0:21:15.760 --> 0:21:19.560 Starting from the time you're growing inside your mother's womb 0:21:19.880 --> 0:21:23.320 as a fetus, your body basically has to start taking sides. 0:21:23.600 --> 0:21:26.840 For example, at some point yourselves have to decide which 0:21:26.880 --> 0:21:30.080 side of your body to grow the heart in. Yes, 0:21:30.160 --> 0:21:31.960 it's not a given that your heart will be on 0:21:32.000 --> 0:21:34.679 the left side of your chest. About one in twelve 0:21:34.720 --> 0:21:39.640 thousand babies conceived half dexterocardia, or the heart on the 0:21:39.720 --> 0:21:42.919 right side of the chest. There have even been cases 0:21:42.960 --> 0:21:45.960 of people finding out late in life that they have it. 0:21:46.320 --> 0:21:48.919 In twenty twenty three, who was reported in a medical 0:21:49.000 --> 0:21:52.000 journal that a perfectly healthy man one hundred and two 0:21:52.080 --> 0:21:55.800 years old went in for cataract surgery and during the 0:21:55.880 --> 0:21:59.000 checkup was stunned to find out his heart was on 0:21:59.080 --> 0:22:02.200 his right side. So you might want to double check 0:22:02.240 --> 0:22:05.240 that your heart is in the right place or the 0:22:05.359 --> 0:22:08.520 left place. I mean, but that's basically what happens with 0:22:08.680 --> 0:22:12.960 left handedness. According to doctor Okelenburg, when your fetus yourselves 0:22:13.080 --> 0:22:16.040 essentially start to pick which side of your brain will 0:22:16.080 --> 0:22:19.640 have the more dominant motor cortex. You can even start 0:22:19.720 --> 0:22:22.600 to see it and which hand the fetus uses. 0:22:22.640 --> 0:22:29.080 More So, if you look at altsound recordings of unborn fetuses, 0:22:29.520 --> 0:22:33.240 you could see that they already have some sort of preference. 0:22:33.280 --> 0:22:36.840 For example, they interact with their left or right hump 0:22:36.880 --> 0:22:38.480 a little bit more than by the other one. And 0:22:38.520 --> 0:22:40.600 if you then wait for the baby to be born 0:22:40.680 --> 0:22:44.960 and test them during school, then these like prenatal preferences 0:22:45.000 --> 0:22:49.160 forehand use predict the writing handedness with more than ninety 0:22:49.200 --> 0:22:50.560 five percent of curiosity. 0:22:51.600 --> 0:22:54.920 Now, scientists aren't really sure why your body picks one 0:22:54.960 --> 0:22:57.480 side or the other. It seems to be a combination 0:22:57.600 --> 0:23:00.840 of genes and hormones, and as we talked about before, 0:23:01.119 --> 0:23:04.439 this can also change after you're born, depending on what 0:23:04.520 --> 0:23:08.359