1 00:00:01,280 --> 00:00:04,960 Speaker 1: Hey, Welcome to Science Stuff, a production of iHeartRadio More. Hey, 2 00:00:05,000 --> 00:00:08,160 Speaker 1: cham And today we're tackling the question what makes someone 3 00:00:08,520 --> 00:00:12,320 Speaker 1: left handed? Is it something in your genes or is 4 00:00:12,360 --> 00:00:15,160 Speaker 1: it random? And why do we involved to have a 5 00:00:15,240 --> 00:00:18,520 Speaker 1: preference for one hand in the first place. We're going 6 00:00:18,560 --> 00:00:21,240 Speaker 1: to talk to two scientists who have spent decades studying 7 00:00:21,280 --> 00:00:23,799 Speaker 1: this phenomenon and who are going to step us through 8 00:00:24,000 --> 00:00:27,160 Speaker 1: what it is, what causes it, and how to tell 9 00:00:27,240 --> 00:00:30,480 Speaker 1: if you're actually left handed. It turns out you could 10 00:00:30,480 --> 00:00:35,839 Speaker 1: have been wrong about it your whole life, So get 11 00:00:35,920 --> 00:00:38,239 Speaker 1: ready to use both sides of your brain as we 12 00:00:38,280 --> 00:00:41,040 Speaker 1: try to get a firm grasp on the right way 13 00:00:41,080 --> 00:00:43,120 Speaker 1: to think about your left hand. 14 00:00:43,920 --> 00:00:44,240 Speaker 2: Enjoy. 15 00:00:46,720 --> 00:00:49,960 Speaker 1: Hey everyone. Today we're talking to two experts, each of 16 00:00:50,000 --> 00:00:54,320 Speaker 1: whom have spent over twenty years studying left handedness. The 17 00:00:54,360 --> 00:00:57,560 Speaker 1: first one is Professor Elka Kraus, and she has a 18 00:00:57,760 --> 00:01:01,440 Speaker 1: very unique job when it comes to handed people. We'll 19 00:01:01,440 --> 00:01:04,080 Speaker 1: talk about what that job is, but first I wanted 20 00:01:04,080 --> 00:01:08,679 Speaker 1: to know what is the actual scientific definition of left handedness. 21 00:01:08,920 --> 00:01:11,920 Speaker 1: As it turns out there is none, at least there's 22 00:01:11,959 --> 00:01:15,360 Speaker 1: no definition scientists can agree on it. So here's my 23 00:01:15,400 --> 00:01:20,360 Speaker 1: conversation with doctor Elka Krauss. Well, thank you doctor Kraus 24 00:01:20,360 --> 00:01:21,000 Speaker 1: for joining us. 25 00:01:21,240 --> 00:01:21,720 Speaker 3: Thank you. 26 00:01:21,760 --> 00:01:23,120 Speaker 1: Can you please tell us who you are and what 27 00:01:23,200 --> 00:01:23,399 Speaker 1: you do. 28 00:01:24,000 --> 00:01:28,000 Speaker 3: I'm a professor for occupational therapy in Germany at University 29 00:01:28,080 --> 00:01:31,720 Speaker 3: for Applied Sciences in Berlin, and one of my research 30 00:01:31,840 --> 00:01:36,880 Speaker 3: topics is handedness. I've been studying it and researching it 31 00:01:37,040 --> 00:01:38,319 Speaker 3: since the nineties. 32 00:01:38,640 --> 00:01:41,039 Speaker 1: Amazing. Are you right handed or left handed? 33 00:01:41,160 --> 00:01:41,919 Speaker 3: I'm right handed. 34 00:01:42,080 --> 00:01:44,280 Speaker 1: Maybe to start us off, can you tell us what 35 00:01:44,440 --> 00:01:47,160 Speaker 1: is handedness and how does it form in people? 36 00:01:47,360 --> 00:01:50,840 Speaker 3: Yeah, so handedness is not just the hand that you 37 00:01:50,960 --> 00:01:53,360 Speaker 3: write with us. Actually it's got two parts. It's the 38 00:01:53,440 --> 00:01:57,000 Speaker 3: hand preference how often you use a hand, And it's 39 00:01:57,040 --> 00:02:00,520 Speaker 3: the hand skill or proficiency, which is relative, so which 40 00:02:00,560 --> 00:02:03,480 Speaker 3: hand is better than the other hand. They say that 41 00:02:03,520 --> 00:02:07,240 Speaker 3: about between ten and twelve percent of humans are left 42 00:02:07,280 --> 00:02:09,960 Speaker 3: handed and the rest is right handed. I see, But 43 00:02:10,280 --> 00:02:12,600 Speaker 3: I just have to say that we have to look 44 00:02:12,600 --> 00:02:16,040 Speaker 3: at that critically because defining handedness is very difficult. It's 45 00:02:16,160 --> 00:02:20,120 Speaker 3: very complex. There's no standard definition of handedness. The way 46 00:02:20,160 --> 00:02:23,079 Speaker 3: it's measured is very different. So some people only look 47 00:02:23,160 --> 00:02:26,959 Speaker 3: at hand preference and the classification. When is a left 48 00:02:26,960 --> 00:02:29,960 Speaker 3: hand or left handed is also not a standard. So 49 00:02:30,240 --> 00:02:33,720 Speaker 3: these are the official numbers of ten to twelve percent 50 00:02:33,840 --> 00:02:37,640 Speaker 3: left handedness, but I personally believe it could be a 51 00:02:37,639 --> 00:02:38,320 Speaker 3: lot higher. 52 00:02:38,840 --> 00:02:41,160 Speaker 1: Why is it difficult to measure handedness? 53 00:02:41,400 --> 00:02:44,400 Speaker 3: Well, people have different ideas of what handedness is. 54 00:02:44,560 --> 00:02:47,600 Speaker 1: I see, it's hard to measure because there's no consensus 55 00:02:47,600 --> 00:02:51,000 Speaker 1: on how to measure it. Yes, so doctor Kraus is 56 00:02:51,000 --> 00:02:54,760 Speaker 1: not your typical scientist. Her interest in what left handedness 57 00:02:54,880 --> 00:02:57,720 Speaker 1: is comes from the very unique job that she has, 58 00:02:58,040 --> 00:03:01,240 Speaker 1: which is to help little kids figure out if they 59 00:03:01,240 --> 00:03:04,680 Speaker 1: are left handed or not. Well. 60 00:03:04,919 --> 00:03:06,880 Speaker 3: The thing is, my context is that I work with 61 00:03:07,040 --> 00:03:10,120 Speaker 3: children who are often on the verge, are going to 62 00:03:10,160 --> 00:03:12,120 Speaker 3: school and who don't know which hand to write with, 63 00:03:12,520 --> 00:03:16,280 Speaker 3: so they come to occupation as therapy to be assessed 64 00:03:16,440 --> 00:03:19,320 Speaker 3: to see what hand should they write with. I see 65 00:03:19,639 --> 00:03:22,760 Speaker 3: the problem is that if children learn to write with 66 00:03:22,919 --> 00:03:26,600 Speaker 3: their non dominant hand, we call them switch handers. We 67 00:03:26,760 --> 00:03:29,280 Speaker 3: know that they can have all sorts of problems because 68 00:03:29,320 --> 00:03:33,119 Speaker 3: of that. They are consequences, and this makes handed there's 69 00:03:33,160 --> 00:03:36,280 Speaker 3: not only a fascinating topic for me, but it actually 70 00:03:36,520 --> 00:03:40,520 Speaker 3: is a very important one because occupation syrrapis in particular 71 00:03:40,800 --> 00:03:43,960 Speaker 3: are co responsible for deciding which hand to write with. 72 00:03:45,240 --> 00:03:47,560 Speaker 1: Okay, you might be thinking, here, it's not that hard 73 00:03:47,560 --> 00:03:50,080 Speaker 1: to figure out which hand you should use to write with. 74 00:03:50,360 --> 00:03:52,760 Speaker 1: You just give a kid a crayon or a pencil 75 00:03:53,040 --> 00:03:55,840 Speaker 1: and see which hand they use. But as we'll talk 76 00:03:55,840 --> 00:03:58,280 Speaker 1: about in a minute, for a lot of kids, it's 77 00:03:58,400 --> 00:04:01,120 Speaker 1: not that simple, and the problem is that making the 78 00:04:01,160 --> 00:04:08,000 Speaker 1: wrong choice can have pretty serious and life altering consequences. Okay, 79 00:04:08,120 --> 00:04:11,560 Speaker 1: you mentioned that there are consequences for kids who are 80 00:04:11,600 --> 00:04:13,920 Speaker 1: forced to use the hand that they're not handed with. 81 00:04:14,400 --> 00:04:17,360 Speaker 3: So, as you might have heard, one hundred years ago, 82 00:04:17,480 --> 00:04:19,960 Speaker 3: people were forced to be right handed, so left hand is. 83 00:04:20,040 --> 00:04:23,080 Speaker 3: At school, they were taught to use the right hand, 84 00:04:23,120 --> 00:04:25,560 Speaker 3: and if they didn't, that left hand was tied behind 85 00:04:25,560 --> 00:04:28,520 Speaker 3: their back or they were actually hit on the hand. 86 00:04:28,760 --> 00:04:31,839 Speaker 3: It was a very strong bias towards right handed, and 87 00:04:31,920 --> 00:04:34,600 Speaker 3: as we speak, you could hear that language is also 88 00:04:34,760 --> 00:04:39,080 Speaker 3: right biased, and so you are right, and it's got 89 00:04:39,080 --> 00:04:42,320 Speaker 3: a bit of a negative thing in all sorts of languages. 90 00:04:42,440 --> 00:04:45,159 Speaker 3: It goes back to a religious thing as well. One 91 00:04:45,200 --> 00:04:48,159 Speaker 3: believe that the left side the devil was looking over 92 00:04:48,200 --> 00:04:50,200 Speaker 3: your shoulder, so if you wrote with your left hand, 93 00:04:50,560 --> 00:04:55,520 Speaker 3: the devil would be able to infuse these evil ideas 94 00:04:55,560 --> 00:04:58,240 Speaker 3: into you. So you were doing the person a big 95 00:04:58,279 --> 00:05:01,240 Speaker 3: favor by forcing them to write with the right hand. 96 00:05:02,040 --> 00:05:05,120 Speaker 3: That caused a lot of painful a lot of left handers. 97 00:05:05,160 --> 00:05:08,240 Speaker 3: Some then started to go back to write with their 98 00:05:08,320 --> 00:05:12,240 Speaker 3: left hand at some point and they found that certain 99 00:05:12,279 --> 00:05:17,840 Speaker 3: problems that they had concentration, memory, retention, also find motor 100 00:05:17,920 --> 00:05:21,520 Speaker 3: coordination or gross motor coordination, you know, whatever they did 101 00:05:21,640 --> 00:05:26,240 Speaker 3: actually became better, which just suddenly they could think free. 102 00:05:27,440 --> 00:05:30,479 Speaker 3: So there's not that much good research on it, like 103 00:05:30,560 --> 00:05:33,440 Speaker 3: control studies and whatever, but we have many sort of 104 00:05:33,520 --> 00:05:37,080 Speaker 3: qualitative data on it. There's been some study on switch 105 00:05:37,160 --> 00:05:40,440 Speaker 3: handers looking at the quality of life, and they did 106 00:05:40,600 --> 00:05:43,960 Speaker 3: find that switch left handers feel that they have a 107 00:05:44,080 --> 00:05:49,720 Speaker 3: lesser quality of life. They are motor proficiency problems, concentration 108 00:05:49,960 --> 00:05:53,800 Speaker 3: learning problems, so they might actually have spelling difficulties, they 109 00:05:53,880 --> 00:05:56,919 Speaker 3: might not remember things. They might be speech problems like 110 00:05:57,040 --> 00:06:03,760 Speaker 3: stuttering going on, and and some moti visceral things like headaches, stomach, 111 00:06:03,839 --> 00:06:08,120 Speaker 3: egche all of that. Because somehow writing, especially writing with 112 00:06:08,200 --> 00:06:11,919 Speaker 3: a non dominant hand, seems to trigger all difficulties. So 113 00:06:12,000 --> 00:06:13,960 Speaker 3: you can imagine if you had to do this, you 114 00:06:14,000 --> 00:06:16,479 Speaker 3: would have to concentrate on so many other things to 115 00:06:16,600 --> 00:06:19,680 Speaker 3: try and sort of get a reasonable result. It will 116 00:06:19,720 --> 00:06:20,640 Speaker 3: never be as. 117 00:06:20,480 --> 00:06:23,560 Speaker 1: Good right right. It'd be like living in a constant 118 00:06:23,600 --> 00:06:28,840 Speaker 1: state of frustration and kind of constant state of feeling 119 00:06:28,880 --> 00:06:32,600 Speaker 1: like there's obstacles. You're thinking, yeah, oh wow, I had 120 00:06:32,640 --> 00:06:36,360 Speaker 1: never thought about how hard that must be. Absolutely, and 121 00:06:36,480 --> 00:06:39,800 Speaker 1: that seems like a very big responsibility to kind of 122 00:06:39,920 --> 00:06:42,880 Speaker 1: direct a kid to use a writer or left Yes, 123 00:06:44,040 --> 00:06:46,240 Speaker 1: I know you might think it can't be that hard 124 00:06:46,279 --> 00:06:48,320 Speaker 1: to tell if a kid is right or left handed, 125 00:06:48,720 --> 00:06:52,840 Speaker 1: but here's the thing. We live in a right handed world. 126 00:06:53,160 --> 00:06:57,320 Speaker 1: Doors are made to be used with your right hand, Toys, 127 00:06:57,440 --> 00:07:02,839 Speaker 1: drinking cups, everything around us is mostly designed for right handers. 128 00:07:03,200 --> 00:07:05,640 Speaker 1: And as a kid, you might see both your parents 129 00:07:05,760 --> 00:07:07,920 Speaker 1: use their right hand to do things, and you might 130 00:07:07,960 --> 00:07:10,600 Speaker 1: think that's the hand I should use. And so there 131 00:07:10,600 --> 00:07:13,080 Speaker 1: are a lot of kids for whom it's not obvious 132 00:07:13,160 --> 00:07:16,240 Speaker 1: whether they're right handed or left handed and which hand 133 00:07:16,320 --> 00:07:17,600 Speaker 1: they should use to write with. 134 00:07:19,160 --> 00:07:21,480 Speaker 3: If you're in a right handed world where everything is 135 00:07:21,560 --> 00:07:25,440 Speaker 3: right hand orientated, then we cannot be sure that we 136 00:07:25,680 --> 00:07:28,120 Speaker 3: just say let's let him write with the right hand, 137 00:07:28,480 --> 00:07:30,200 Speaker 3: or let her write with the right hand because we 138 00:07:30,280 --> 00:07:34,000 Speaker 3: might be switching somebody, usually a left handed So you 139 00:07:34,040 --> 00:07:37,520 Speaker 3: can see that my point of departure is not just 140 00:07:37,840 --> 00:07:42,200 Speaker 3: looking at handedness as a phenomenon, but it's actually identifying 141 00:07:42,280 --> 00:07:45,840 Speaker 3: those children who might be left handers and preventing them 142 00:07:45,840 --> 00:07:50,760 Speaker 3: from switching, or identifying switched handers and maybe reverting them 143 00:07:50,800 --> 00:07:52,559 Speaker 3: back to their dominant hand. 144 00:07:52,840 --> 00:07:56,600 Speaker 1: I see. Now, as doctor Krauss mentioned, there is no 145 00:07:56,840 --> 00:08:01,120 Speaker 1: single definition of what left handedness is, but there are 146 00:08:01,240 --> 00:08:06,640 Speaker 1: tends you can take that measure your handedness along several dimensions. 147 00:08:08,480 --> 00:08:12,720 Speaker 3: So in my work, I've actually defined six dimensions off handedness. 148 00:08:12,760 --> 00:08:15,920 Speaker 1: What are these six dimensions that you measure left handedness on? 149 00:08:16,400 --> 00:08:19,520 Speaker 3: So, as I said the first two, the most important 150 00:08:19,640 --> 00:08:23,400 Speaker 3: ones would be that you have preference and skill. You 151 00:08:23,440 --> 00:08:26,000 Speaker 3: would think that would be the same thing, but it's 152 00:08:26,080 --> 00:08:28,720 Speaker 3: not always that your preferred hand is also your better hand. 153 00:08:29,280 --> 00:08:32,120 Speaker 1: Really, what, yes. 154 00:08:31,920 --> 00:08:33,319 Speaker 3: Are you right handed or left handed? 155 00:08:33,360 --> 00:08:35,960 Speaker 1: May I ask I'm right handed? Or wait? If you 156 00:08:35,960 --> 00:08:37,679 Speaker 1: had to guess, would you be able to guess? 157 00:08:37,920 --> 00:08:43,720 Speaker 3: No? But this is the thing. Right handed don't understand 158 00:08:43,720 --> 00:08:47,000 Speaker 3: this necessary. They think that left handedness must be the 159 00:08:47,000 --> 00:08:49,760 Speaker 3: opposite of right handedness. So anyway, Those are the two 160 00:08:49,800 --> 00:08:54,079 Speaker 3: first dimensions. The second two are direction and then very 161 00:08:54,120 --> 00:08:58,360 Speaker 3: importantly the extent of handedness. So you have hands, as 162 00:08:58,400 --> 00:09:01,520 Speaker 3: I call them, that of verse very strongly handed. The 163 00:09:01,600 --> 00:09:03,679 Speaker 3: right hander is that do everything right, left handed that 164 00:09:03,760 --> 00:09:07,080 Speaker 3: do everything left. But that is actually the minority of people. 165 00:09:07,600 --> 00:09:11,520 Speaker 3: Most people are moderately. The extent of hand is moderate. 166 00:09:11,679 --> 00:09:14,079 Speaker 3: And then you have quite a big group in left 167 00:09:14,080 --> 00:09:18,160 Speaker 3: handers that are very slightly left handed. They're not strongly 168 00:09:18,240 --> 00:09:20,080 Speaker 3: left handed, that do a lot of things with the 169 00:09:20,160 --> 00:09:23,560 Speaker 3: right hand really, and people don't understand that, and they 170 00:09:23,679 --> 00:09:26,320 Speaker 3: called the mixed handers, but they're actually left handed. So 171 00:09:26,480 --> 00:09:28,560 Speaker 3: there are some researchers that found that this group of 172 00:09:28,640 --> 00:09:30,800 Speaker 3: left handers, they will always write with their left hand, 173 00:09:31,120 --> 00:09:33,760 Speaker 3: but they might do more than half the things with 174 00:09:33,840 --> 00:09:34,440 Speaker 3: the right hand. 175 00:09:34,520 --> 00:09:35,400 Speaker 1: WHOA. 176 00:09:36,559 --> 00:09:40,280 Speaker 3: We see this when we actually do differentiated assessments. So 177 00:09:40,360 --> 00:09:44,839 Speaker 3: again there is this complex play or symphony of these 178 00:09:44,840 --> 00:09:48,520 Speaker 3: different dimensions. Actually then determine which hand you use. 179 00:09:49,040 --> 00:09:53,880 Speaker 1: WHOA. It's a lot more complicated than maye people think. Absolutely, 180 00:09:56,000 --> 00:09:59,280 Speaker 1: it seems like you have these dimensions because some people 181 00:09:59,360 --> 00:10:02,040 Speaker 1: might score high and based on one dimension, you might say, oh, 182 00:10:02,120 --> 00:10:04,320 Speaker 1: this person's right handed, or left handed, but on another 183 00:10:04,360 --> 00:10:08,800 Speaker 1: dimension it might be different. Yes, I see, And so 184 00:10:08,960 --> 00:10:10,680 Speaker 1: what that tells you is that it's sort of a 185 00:10:10,760 --> 00:10:13,760 Speaker 1: complicated thing and it's sort of on a spectrum. Is 186 00:10:13,760 --> 00:10:16,480 Speaker 1: that kind of a big takeaway is that it's not 187 00:10:16,600 --> 00:10:19,319 Speaker 1: just a right or left. There's sort of a lot 188 00:10:19,360 --> 00:10:21,800 Speaker 1: of handedness in between. That's right. 189 00:10:22,080 --> 00:10:25,320 Speaker 3: I think handedness is a continuum. So if you have 190 00:10:25,559 --> 00:10:29,520 Speaker 3: extreme left, extreme right and somewhere you know, if every 191 00:10:29,559 --> 00:10:31,560 Speaker 3: person is somewhere in between. 192 00:10:31,760 --> 00:10:34,960 Speaker 1: Wow, But I guess we like binary things, so we 193 00:10:35,080 --> 00:10:37,920 Speaker 1: might draw a line where it's right or left, but 194 00:10:38,000 --> 00:10:41,320 Speaker 1: really it's a richer picture. Yes, people can have a 195 00:10:41,400 --> 00:10:45,439 Speaker 1: preference for right left more or less, but it may 196 00:10:45,480 --> 00:10:48,760 Speaker 1: not necessarily correlate to which hand is better at doing things. 197 00:10:49,080 --> 00:10:49,520 Speaker 3: Yeah. 198 00:10:49,559 --> 00:10:52,760 Speaker 1: Wow, I had to realize it's so complicated. 199 00:10:52,240 --> 00:10:54,280 Speaker 3: Nor did I honestly when I started. 200 00:10:54,840 --> 00:10:59,640 Speaker 1: Really wow, I have no idea all right. So there 201 00:10:59,679 --> 00:11:03,400 Speaker 1: is no single definition of what left handedness is, and 202 00:11:03,679 --> 00:11:06,520 Speaker 1: in fact, it seems to be on a spectrum. Some 203 00:11:06,559 --> 00:11:09,520 Speaker 1: people are more left or right handed than others, And 204 00:11:09,640 --> 00:11:13,200 Speaker 1: it's entirely possible that you could be a hidden left 205 00:11:13,200 --> 00:11:16,439 Speaker 1: handed person and you only think you're right handed because 206 00:11:16,600 --> 00:11:19,240 Speaker 1: that's what you were taught as a little kid. But 207 00:11:19,280 --> 00:11:22,559 Speaker 1: here's the question, why are we handed in the first place? 208 00:11:23,000 --> 00:11:25,640 Speaker 1: Why do we tend to have a preference, however strong 209 00:11:25,679 --> 00:11:28,880 Speaker 1: it may be, to use one hand and not the other. 210 00:11:29,440 --> 00:11:32,120 Speaker 1: Is it programmed in our genes? And why did we 211 00:11:32,200 --> 00:11:36,560 Speaker 1: evolve this tendency to prefer one hand. When we come back, 212 00:11:36,800 --> 00:11:39,640 Speaker 1: we're going to try our hand at answering these questions. 213 00:11:40,040 --> 00:11:56,600 Speaker 1: So stay with us. We'll be right back. Hey, welcome back. 214 00:11:57,040 --> 00:12:00,400 Speaker 1: We're talking about left handedness, and so far are we've 215 00:12:00,440 --> 00:12:03,360 Speaker 1: talked about how hard it is to actually define it. 216 00:12:03,760 --> 00:12:06,840 Speaker 1: Now we're going to talk about what actually causes it. 217 00:12:06,880 --> 00:12:10,760 Speaker 1: Is it hereditary or random? Or are there other reasons 218 00:12:10,840 --> 00:12:13,520 Speaker 1: why you choose to use one hand over the other. 219 00:12:14,040 --> 00:12:16,520 Speaker 1: To help answer these questions, I reached out to another 220 00:12:16,600 --> 00:12:21,120 Speaker 1: scientist who spent decades studying this phenomenon. Here's my conversation 221 00:12:21,200 --> 00:12:25,200 Speaker 1: with doctor Sebastian Oglenburg. Well, thank you so much for 222 00:12:25,280 --> 00:12:26,599 Speaker 1: joining us at you're Okenburg. 223 00:12:26,880 --> 00:12:29,920 Speaker 4: Thank you so much for inviting me. I'm a germ 224 00:12:30,000 --> 00:12:34,400 Speaker 4: professor of a research method in psychology at medical school 225 00:12:34,840 --> 00:12:38,440 Speaker 4: in Hamburg and Northern Germany, and I spent the last 226 00:12:38,480 --> 00:12:42,960 Speaker 4: twenty years doing research on left handedness and vainness symmetries. 227 00:12:43,320 --> 00:12:47,280 Speaker 4: So I'm really interested in understanding why people are left 228 00:12:47,320 --> 00:12:49,480 Speaker 4: tended and what it means to be left handed. 229 00:12:49,679 --> 00:12:51,600 Speaker 1: Amazing that's perfect for us today. 230 00:12:52,360 --> 00:12:56,040 Speaker 4: So left tendedness is, of course, on the surface, it's 231 00:12:56,120 --> 00:12:59,920 Speaker 4: a preference in behavior, like people who are left tended 232 00:13:00,160 --> 00:13:02,520 Speaker 4: like to use their left hand to do things like 233 00:13:02,760 --> 00:13:07,360 Speaker 4: writing or drawing or using scissors. But handedness has nothing 234 00:13:07,440 --> 00:13:11,199 Speaker 4: to do with the hands themselves, despite the name. If 235 00:13:11,200 --> 00:13:14,439 Speaker 4: you ever looked at the hands the left hand and 236 00:13:14,559 --> 00:13:17,600 Speaker 4: right hand, you would not be able to distinguish just 237 00:13:17,960 --> 00:13:20,840 Speaker 4: by looking at the hand whose left handed, whose right 238 00:13:20,880 --> 00:13:21,440 Speaker 4: handed right? 239 00:13:21,480 --> 00:13:23,400 Speaker 2: So they're looking pretty identical. 240 00:13:23,640 --> 00:13:27,360 Speaker 4: So handedness is something that has not much to do 241 00:13:27,400 --> 00:13:30,920 Speaker 4: with the hands, but a lot to do with the brain. 242 00:13:31,440 --> 00:13:35,200 Speaker 4: So what handedness is is a form of so called 243 00:13:35,240 --> 00:13:40,280 Speaker 4: hemispheric asymmetries, meaning that our brain has two halves, and 244 00:13:40,400 --> 00:13:43,840 Speaker 4: these two halves both do amazing things, but they do 245 00:13:43,920 --> 00:13:47,720 Speaker 4: a little bit different things, and handedness is one form 246 00:13:47,800 --> 00:13:48,920 Speaker 4: of these symmetries. 247 00:13:49,480 --> 00:13:51,920 Speaker 1: Can you give us other examples of brain asymmetries. 248 00:13:52,400 --> 00:13:55,600 Speaker 4: So these brain asymmetries are quite common, and there's a 249 00:13:55,679 --> 00:13:58,520 Speaker 4: lot of things in a brain that are asymmetric. The 250 00:13:58,559 --> 00:14:02,000 Speaker 4: most well known example language, so we know that for 251 00:14:02,160 --> 00:14:07,080 Speaker 4: most people, language to speaking to other people and understanding 252 00:14:07,080 --> 00:14:12,360 Speaker 4: what they're saying is controlled largely, not exclusively, by the 253 00:14:12,440 --> 00:14:15,040 Speaker 4: left side of the brain. So for example, if you 254 00:14:15,320 --> 00:14:19,400 Speaker 4: ever had a relative who suffered a stroke to the 255 00:14:19,520 --> 00:14:23,960 Speaker 4: left side of the brain, they have severe problems with 256 00:14:24,080 --> 00:14:27,480 Speaker 4: speaking in the weeks and months after they had the stroke. 257 00:14:27,800 --> 00:14:31,840 Speaker 4: People who have a right sided stroke typically do not 258 00:14:31,920 --> 00:14:36,240 Speaker 4: have this language problem. Other things that are quite come 259 00:14:36,560 --> 00:14:40,600 Speaker 4: are the processing of faces. So for me, like to 260 00:14:40,760 --> 00:14:44,800 Speaker 4: recognize your face, this is something that is mostly done 261 00:14:45,000 --> 00:14:48,920 Speaker 4: by my right hemisphere, so it's a specific area called 262 00:14:48,920 --> 00:14:53,040 Speaker 4: the fusiform face area that is located on the right 263 00:14:53,120 --> 00:14:56,160 Speaker 4: side in most people, and so on. So there are 264 00:14:56,160 --> 00:15:01,480 Speaker 4: many other things like visospatial attention, recognizing bodies of other people, 265 00:15:01,640 --> 00:15:06,160 Speaker 4: mathematical operations, so a lot of things that are complicated 266 00:15:06,240 --> 00:15:10,920 Speaker 4: and hard to do are organized in asymmetric networks, and 267 00:15:11,000 --> 00:15:14,200 Speaker 4: handedness is one form of these the symmetry so it 268 00:15:14,240 --> 00:15:19,280 Speaker 4: is a dominance of the motocortex, so the brain areas 269 00:15:19,320 --> 00:15:23,600 Speaker 4: that are controlling our movements for things like writing, drawing, 270 00:15:23,720 --> 00:15:26,600 Speaker 4: and so on. What we would call fine motor movements. 271 00:15:27,240 --> 00:15:31,880 Speaker 4: So left handers have a right hemispheric motor dominance body 272 00:15:31,880 --> 00:15:36,520 Speaker 4: sphinx and right handers a left hemispheric dominance because the 273 00:15:36,640 --> 00:15:39,520 Speaker 4: left side of the brain is controlling the right side 274 00:15:39,560 --> 00:15:41,320 Speaker 4: of the body and vice versa. 275 00:15:42,480 --> 00:15:45,120 Speaker 1: WHOA, what does it mean dominant? It means it's better 276 00:15:45,160 --> 00:15:48,760 Speaker 1: at things, or it it just kind of asserts control 277 00:15:48,840 --> 00:15:50,320 Speaker 1: of things. What does dominant mean? 278 00:15:50,720 --> 00:15:52,320 Speaker 2: It means several things. 279 00:15:52,360 --> 00:15:55,320 Speaker 4: So for the one part, it means if you like 280 00:15:55,680 --> 00:15:59,800 Speaker 4: decide consciously or subconsciously, like you want to draw a picture, 281 00:16:00,160 --> 00:16:04,880 Speaker 4: then generally you would decide for your dominant hands. So 282 00:16:04,960 --> 00:16:07,960 Speaker 4: on one part of it, it is a preference that 283 00:16:08,040 --> 00:16:11,680 Speaker 4: you're having as a person. But this preference also goes 284 00:16:11,800 --> 00:16:15,600 Speaker 4: along with differences in skill. So even if you would 285 00:16:15,640 --> 00:16:18,880 Speaker 4: like draw with your nondamental left hand, you would not 286 00:16:19,000 --> 00:16:21,920 Speaker 4: be able as much as you try to make the 287 00:16:22,000 --> 00:16:26,280 Speaker 4: same quality of drawing, so there is a difference in skill. 288 00:16:27,200 --> 00:16:32,040 Speaker 4: There's also neurobiological differences. So typically in a right hander, 289 00:16:32,240 --> 00:16:35,160 Speaker 4: so the part of the motor cortex is representing the 290 00:16:35,280 --> 00:16:39,840 Speaker 4: hand would be larger and have differential connections. So it's 291 00:16:39,840 --> 00:16:43,960 Speaker 4: something that also develops over the course of your lifetime 292 00:16:44,040 --> 00:16:48,520 Speaker 4: because your networks are not like completely fixed at birth. 293 00:16:49,040 --> 00:16:52,720 Speaker 4: By you know, using your dominant hand more over your lifetime, 294 00:16:52,800 --> 00:16:56,640 Speaker 4: you also strengthen connections to other networks in your brain. 295 00:16:57,160 --> 00:17:01,280 Speaker 4: So it's the mixture of preference, skill, ill you're adda 296 00:17:01,400 --> 00:17:06,119 Speaker 4: to me, and folastic training processes over the coursing f 297 00:17:06,119 --> 00:17:06,520 Speaker 4: life time. 298 00:17:06,600 --> 00:17:12,600 Speaker 1: Wow, that is very complicated. So handedness is a property 299 00:17:12,640 --> 00:17:16,120 Speaker 1: of your brain, not your actual hands, and it has 300 00:17:16,160 --> 00:17:18,280 Speaker 1: to do with the fact that your brain, for a 301 00:17:18,320 --> 00:17:22,240 Speaker 1: lot of things, is a symmetrical It has two sides, 302 00:17:22,280 --> 00:17:25,280 Speaker 1: and one side just happens to be more dominant for 303 00:17:25,359 --> 00:17:28,359 Speaker 1: how you plan to move your body. For right handed people, 304 00:17:28,400 --> 00:17:30,720 Speaker 1: it's the left side of your brain, and for left 305 00:17:30,720 --> 00:17:34,080 Speaker 1: handed people it's the right side of the brain. Of course, 306 00:17:34,200 --> 00:17:36,800 Speaker 1: Now the question is what causes one side of your 307 00:17:36,840 --> 00:17:39,520 Speaker 1: brain to be more dominant and why is it that 308 00:17:39,600 --> 00:17:42,000 Speaker 1: ninety percent of the time it ends up making people 309 00:17:42,200 --> 00:17:45,080 Speaker 1: right handed versus ten percent of the time it makes 310 00:17:45,119 --> 00:17:51,640 Speaker 1: them left handed. What causes left handedness? Like what causes 311 00:17:52,400 --> 00:17:55,280 Speaker 1: for a right handed person, I need that left brain 312 00:17:55,920 --> 00:17:59,000 Speaker 1: preference and skill and eventual training. 313 00:17:59,320 --> 00:18:02,640 Speaker 4: So we know this is odso not as simple as 314 00:18:02,800 --> 00:18:08,480 Speaker 4: people thought. So it is a trade that has substantial 315 00:18:08,680 --> 00:18:13,560 Speaker 4: genetic contributions but also non genetic contributions. So there's a 316 00:18:13,600 --> 00:18:19,159 Speaker 4: lot of exciting, large scale cooperative research that has shown 317 00:18:19,280 --> 00:18:24,199 Speaker 4: that there's about forty eight locations in the genome that 318 00:18:24,320 --> 00:18:25,840 Speaker 4: are relevant for handedness. 319 00:18:26,000 --> 00:18:28,960 Speaker 2: You said, so it's forty eight. 320 00:18:29,040 --> 00:18:34,240 Speaker 4: That the play roles quite interesting that the familial handedness 321 00:18:34,440 --> 00:18:36,879 Speaker 4: has a strong effect on the child's handedness. 322 00:18:36,920 --> 00:18:39,360 Speaker 2: With two left handed parents would. 323 00:18:39,280 --> 00:18:41,760 Speaker 4: Get a child, the child as a much higher chance 324 00:18:41,800 --> 00:18:44,320 Speaker 4: with also being left handed than the child of two 325 00:18:44,520 --> 00:18:47,439 Speaker 4: right handed parents, And the same goes if there's just 326 00:18:47,560 --> 00:18:50,719 Speaker 4: like one right handed one left handed parent, and the 327 00:18:50,840 --> 00:18:52,160 Speaker 4: child would be intermediate. 328 00:18:53,560 --> 00:18:53,960 Speaker 2: I see. 329 00:18:53,960 --> 00:18:56,840 Speaker 1: Do we have a sense of what percentage left handedness 330 00:18:57,000 --> 00:18:58,280 Speaker 1: is due to genetics? 331 00:18:58,359 --> 00:19:03,160 Speaker 4: So we know from in studies and from other family 332 00:19:03,280 --> 00:19:07,640 Speaker 4: studies it's probably around twenty five percent, which would mean 333 00:19:07,680 --> 00:19:10,720 Speaker 4: there are seventy five percent of factors that are not 334 00:19:10,840 --> 00:19:14,400 Speaker 4: directly explained by it. Wow, But it's also not generally 335 00:19:14,560 --> 00:19:17,960 Speaker 4: very well understood whether remaining a seventy. 336 00:19:17,600 --> 00:19:20,000 Speaker 2: Five percent come from I see. 337 00:19:20,160 --> 00:19:24,560 Speaker 4: So they seem to be like sort of individual biological 338 00:19:24,880 --> 00:19:28,399 Speaker 4: processes in a person that happens that might also be 339 00:19:28,560 --> 00:19:31,359 Speaker 4: due to genetics, but are not caught very well, and 340 00:19:31,440 --> 00:19:36,520 Speaker 4: these like twin family designed. So there's an ongoing discussion 341 00:19:36,880 --> 00:19:40,359 Speaker 4: about this percentage because it seems to be quite low, 342 00:19:40,800 --> 00:19:41,640 Speaker 4: so it might be higher. 343 00:19:41,720 --> 00:19:44,760 Speaker 1: In fact, I see it might be higher than twenty 344 00:19:44,760 --> 00:19:48,200 Speaker 1: five percent genetic, but not necessarily meaning the cost could 345 00:19:48,240 --> 00:19:53,440 Speaker 1: be more genetic, but we don't know. Yes, yes, left 346 00:19:53,440 --> 00:19:57,320 Speaker 1: handedness is not completely genetic. If both of your parents 347 00:19:57,359 --> 00:19:59,960 Speaker 1: are left handed, then you do have a higher chance 348 00:20:00,240 --> 00:20:04,240 Speaker 1: also being left handed, but it's not guaranteed. According to 349 00:20:04,240 --> 00:20:08,080 Speaker 1: our experts, there's no one gene that makes you left handed. 350 00:20:08,440 --> 00:20:11,880 Speaker 1: Scientists have found forty eight gens that seem to be involved, 351 00:20:12,119 --> 00:20:16,280 Speaker 1: and they only predict about twenty five percent of left handedness. 352 00:20:16,640 --> 00:20:19,080 Speaker 1: The rest could be things in your environment. 353 00:20:20,000 --> 00:20:23,960 Speaker 4: There are also a couple of environmental, non genetic factors 354 00:20:24,000 --> 00:20:27,760 Speaker 4: that play a role. For example, gender actually does so 355 00:20:27,920 --> 00:20:31,760 Speaker 4: men are more likely to be left handed than women. 356 00:20:32,560 --> 00:20:36,640 Speaker 4: There's also a couple other things, for example, people who 357 00:20:36,680 --> 00:20:39,840 Speaker 4: have been like rest fed and for a higher chance 358 00:20:40,000 --> 00:20:41,040 Speaker 4: of being right handed. 359 00:20:41,280 --> 00:20:44,720 Speaker 1: Ah, so breastfeeding has something to do with it. 360 00:20:45,160 --> 00:20:47,600 Speaker 4: Yeah, it's a very curious finding. So it seems to 361 00:20:47,640 --> 00:20:51,359 Speaker 4: be a rather strong effect, which I don't think is 362 00:20:51,440 --> 00:20:55,879 Speaker 4: well understood on a neurobiological level, but it seems to 363 00:20:55,920 --> 00:20:59,840 Speaker 4: be there's an early effect of some sexophmoons on hand 364 00:21:00,160 --> 00:21:02,800 Speaker 4: that's development of brainer symmetries. 365 00:21:03,880 --> 00:21:06,920 Speaker 1: So the basic picture here is that handedness. Whether you 366 00:21:07,000 --> 00:21:09,520 Speaker 1: prefer to use your right or left hand, but whether 367 00:21:09,560 --> 00:21:12,640 Speaker 1: one hand is more skilled than the other, is all 368 00:21:12,640 --> 00:21:15,439 Speaker 1: in your brain, and a lot can happen to your brain. 369 00:21:15,760 --> 00:21:19,560 Speaker 1: Starting from the time you're growing inside your mother's womb 370 00:21:19,880 --> 00:21:23,320 Speaker 1: as a fetus, your body basically has to start taking sides. 371 00:21:23,600 --> 00:21:26,840 Speaker 1: For example, at some point yourselves have to decide which 372 00:21:26,880 --> 00:21:30,080 Speaker 1: side of your body to grow the heart in. Yes, 373 00:21:30,160 --> 00:21:31,960 Speaker 1: it's not a given that your heart will be on 374 00:21:32,000 --> 00:21:34,679 Speaker 1: the left side of your chest. About one in twelve 375 00:21:34,720 --> 00:21:39,640 Speaker 1: thousand babies conceived half dexterocardia, or the heart on the 376 00:21:39,720 --> 00:21:42,919 Speaker 1: right side of the chest. There have even been cases 377 00:21:42,960 --> 00:21:45,960 Speaker 1: of people finding out late in life that they have it. 378 00:21:46,320 --> 00:21:48,919 Speaker 1: In twenty twenty three, who was reported in a medical 379 00:21:49,000 --> 00:21:52,000 Speaker 1: journal that a perfectly healthy man one hundred and two 380 00:21:52,080 --> 00:21:55,800 Speaker 1: years old went in for cataract surgery and during the 381 00:21:55,880 --> 00:21:59,000 Speaker 1: checkup was stunned to find out his heart was on 382 00:21:59,080 --> 00:22:02,200 Speaker 1: his right side. So you might want to double check 383 00:22:02,240 --> 00:22:05,240 Speaker 1: that your heart is in the right place or the 384 00:22:05,359 --> 00:22:08,520 Speaker 1: left place. I mean, but that's basically what happens with 385 00:22:08,680 --> 00:22:12,960 Speaker 1: left handedness. According to doctor Okelenburg, when your fetus yourselves 386 00:22:13,080 --> 00:22:16,040 Speaker 1: essentially start to pick which side of your brain will 387 00:22:16,080 --> 00:22:19,640 Speaker 1: have the more dominant motor cortex. You can even start 388 00:22:19,720 --> 00:22:22,600 Speaker 1: to see it and which hand the fetus uses. 389 00:22:22,640 --> 00:22:29,080 Speaker 4: More So, if you look at altsound recordings of unborn fetuses, 390 00:22:29,520 --> 00:22:33,240 Speaker 4: you could see that they already have some sort of preference. 391 00:22:33,280 --> 00:22:36,840 Speaker 4: For example, they interact with their left or right hump 392 00:22:36,880 --> 00:22:38,480 Speaker 4: a little bit more than by the other one. And 393 00:22:38,520 --> 00:22:40,600 Speaker 4: if you then wait for the baby to be born 394 00:22:40,680 --> 00:22:44,960 Speaker 4: and test them during school, then these like prenatal preferences 395 00:22:45,000 --> 00:22:49,160 Speaker 4: forehand use predict the writing handedness with more than ninety 396 00:22:49,200 --> 00:22:50,560 Speaker 4: five percent of curiosity. 397 00:22:51,600 --> 00:22:54,920 Speaker 1: Now, scientists aren't really sure why your body picks one 398 00:22:54,960 --> 00:22:57,480 Speaker 1: side or the other. It seems to be a combination 399 00:22:57,600 --> 00:23:00,840 Speaker 1: of genes and hormones, and as we talked about before, 400 00:23:01,119 --> 00:23:04,439 Speaker 1: this can also change after you're born, depending on what 401 00:23:04,520 --> 00:23:08,359 Speaker 1: you're tagged as a kid. But here's the next big question, 402 00:23:08,800 --> 00:23:12,439 Speaker 1: why even pick aside at all? What's the point of 403 00:23:12,520 --> 00:23:16,560 Speaker 1: being handed? Why couldn't we all just be Ambidexter's or 404 00:23:16,760 --> 00:23:19,160 Speaker 1: just as good with the left hand as the right hand. 405 00:23:19,560 --> 00:23:23,040 Speaker 1: Why did humans evolve to have a hand preference? And 406 00:23:23,200 --> 00:23:25,919 Speaker 1: are we the only animal in nature the ad has it. 407 00:23:26,960 --> 00:23:29,119 Speaker 1: When we come back, I'll hand it over to our 408 00:23:29,160 --> 00:23:32,480 Speaker 1: experts to answer these questions. So don't lose your grip 409 00:23:32,560 --> 00:23:51,000 Speaker 1: on this podcast. We'll be right back. Hey, we'll come back. 410 00:23:51,280 --> 00:23:54,280 Speaker 1: We're talking about left handedness with two scientists, and so 411 00:23:54,400 --> 00:23:57,080 Speaker 1: far we've learned that the handedness sort of lies on 412 00:23:57,119 --> 00:24:00,199 Speaker 1: a spectrum. Most people are strongly right hand and that 413 00:24:00,520 --> 00:24:03,760 Speaker 1: a few people are strongly left handed, and some people 414 00:24:03,800 --> 00:24:07,200 Speaker 1: are somewhere in between. We also learned scientists aren't sure 415 00:24:07,359 --> 00:24:11,920 Speaker 1: what causes handedness. There are about forty eight genes associated 416 00:24:11,960 --> 00:24:14,640 Speaker 1: with it, but how those genes affect which of your 417 00:24:14,680 --> 00:24:17,760 Speaker 1: mortar cortex areas turns out to be the dominant one 418 00:24:18,240 --> 00:24:21,879 Speaker 1: is still a mystery. And apparently these genes only account 419 00:24:21,920 --> 00:24:24,840 Speaker 1: for about twenty five percent of whether you're right or 420 00:24:24,920 --> 00:24:28,920 Speaker 1: left handed. The other seventy five percent could be environmental 421 00:24:28,960 --> 00:24:32,880 Speaker 1: factors or hidden deeper in your genetic code. But now 422 00:24:32,880 --> 00:24:35,679 Speaker 1: we're going to tackle an even bigger question, which is 423 00:24:36,240 --> 00:24:38,840 Speaker 1: why are we handed in the first place, I mean, 424 00:24:39,000 --> 00:24:43,640 Speaker 1: why pick aside, why aren't we all ambi dextrics. As 425 00:24:43,680 --> 00:24:46,720 Speaker 1: it turns out, humans are not the only animal that 426 00:24:47,160 --> 00:24:52,400 Speaker 1: takes up paw. You've written about the idea that there's 427 00:24:52,480 --> 00:24:55,160 Speaker 1: handedness or potness in animals. 428 00:24:55,359 --> 00:24:57,800 Speaker 2: Yeah, so in general, I've worked a lot on this. 429 00:24:58,680 --> 00:25:01,560 Speaker 4: I think back in the day, people always thought did 430 00:25:01,680 --> 00:25:05,679 Speaker 4: only humans show handedness? Because all humans right, But of 431 00:25:05,720 --> 00:25:08,720 Speaker 4: course you cannot have a look at the writing patterns 432 00:25:08,760 --> 00:25:10,920 Speaker 4: of a cat because they rarely use pets. 433 00:25:12,320 --> 00:25:13,880 Speaker 2: But at some point people. 434 00:25:13,760 --> 00:25:18,720 Speaker 4: Started to look at poor preferences or flipper preferences or 435 00:25:18,760 --> 00:25:23,960 Speaker 4: whatever in animals, using experimental designs that would allow them 436 00:25:24,080 --> 00:25:28,000 Speaker 4: to actually measure normal behavior. 437 00:25:27,359 --> 00:25:28,240 Speaker 2: Of the animal. 438 00:25:28,280 --> 00:25:31,760 Speaker 4: And what you find, Dan is that most animal species 439 00:25:32,000 --> 00:25:36,960 Speaker 4: actually show left and right handedness. So asn enormous amount 440 00:25:37,040 --> 00:25:39,240 Speaker 4: of studies on that. It's just just like more than 441 00:25:39,240 --> 00:25:42,800 Speaker 4: one hundred different species it's been investigated, and I think 442 00:25:42,840 --> 00:25:46,800 Speaker 4: the general pattern is that a lot of species show 443 00:25:46,920 --> 00:25:49,119 Speaker 4: sort of like individual preferences. 444 00:25:49,560 --> 00:25:50,440 Speaker 2: So if you. 445 00:25:50,400 --> 00:25:55,399 Speaker 4: Look at a cat, most cats would have rather strong preference. 446 00:25:54,960 --> 00:25:57,040 Speaker 2: For the right side or the left side. 447 00:25:57,080 --> 00:25:58,919 Speaker 4: So what you could do, for example, if you have 448 00:25:59,000 --> 00:26:00,880 Speaker 4: a cat at home, you want who knows the cat 449 00:26:01,000 --> 00:26:03,680 Speaker 4: left port the right port. You could do something it's 450 00:26:03,680 --> 00:26:06,560 Speaker 4: called the food reaching task. So you take like the 451 00:26:06,640 --> 00:26:10,879 Speaker 4: little inlet from a toilet paper roll, close up one 452 00:26:10,920 --> 00:26:13,800 Speaker 4: side with a little bit of like a cling wrap 453 00:26:13,920 --> 00:26:16,280 Speaker 4: foil or whatever, and then you put like some like 454 00:26:16,520 --> 00:26:20,000 Speaker 4: cat food tokens into this toilet paper roll and just 455 00:26:20,040 --> 00:26:22,680 Speaker 4: have a look whether the cat is reaching into it 456 00:26:22,720 --> 00:26:25,119 Speaker 4: with the left or the right paw. So if you 457 00:26:25,240 --> 00:26:29,760 Speaker 4: use these kind of things, you typically find that individual 458 00:26:29,920 --> 00:26:33,639 Speaker 4: cat has portaners. But in generally for a lot of 459 00:26:33,720 --> 00:26:37,520 Speaker 4: animal species, left portners is more common than in humans. 460 00:26:37,560 --> 00:26:41,719 Speaker 4: So we had this large meta analysis in twenty twenty 461 00:26:41,760 --> 00:26:45,840 Speaker 4: about human handedness showing it's ten point six a percent 462 00:26:45,880 --> 00:26:48,600 Speaker 4: of people are left handed, but if you look at 463 00:26:48,640 --> 00:26:52,160 Speaker 4: cats or dogs, it's more like thirty to forty percent 464 00:26:52,200 --> 00:26:55,919 Speaker 4: of animals being left pot So it seems to be 465 00:26:56,400 --> 00:27:00,600 Speaker 4: animals do have handedness, but for a lot of animals species, 466 00:27:01,400 --> 00:27:05,360 Speaker 4: left handedness left partners is much more common than in humans, 467 00:27:05,359 --> 00:27:09,560 Speaker 4: so it goes more into like an equal distribution. There's 468 00:27:09,600 --> 00:27:13,520 Speaker 4: also research with animals in the laboratory. So for example, 469 00:27:13,680 --> 00:27:17,359 Speaker 4: people go to cat or dog hotels and ask the 470 00:27:17,400 --> 00:27:20,480 Speaker 4: owners whether they can test their animals there while the 471 00:27:20,600 --> 00:27:24,120 Speaker 4: owner's own vocation do a little bit of like interactions 472 00:27:24,160 --> 00:27:26,800 Speaker 4: with them and then find out whether they're left or 473 00:27:26,880 --> 00:27:29,879 Speaker 4: right port and be for example, also have some like 474 00:27:29,960 --> 00:27:33,800 Speaker 4: citizen science projects where we ask people to record their 475 00:27:34,240 --> 00:27:37,520 Speaker 4: animals with a smartphone while they are doing. 476 00:27:37,520 --> 00:27:39,280 Speaker 2: Basically the scientific work. 477 00:27:40,000 --> 00:27:43,679 Speaker 4: So there is a really big amount of research on 478 00:27:43,960 --> 00:27:48,119 Speaker 4: animal hotness and handedness and generally shows humans are not 479 00:27:48,680 --> 00:27:50,920 Speaker 4: unique or special in that. 480 00:27:50,960 --> 00:27:53,359 Speaker 2: They have handedness. Most animal species have. 481 00:27:53,480 --> 00:27:55,840 Speaker 1: It too, I see, but we're sort of unique in 482 00:27:56,000 --> 00:27:59,800 Speaker 1: how much more prevalient right handedness is. 483 00:28:00,119 --> 00:28:02,320 Speaker 2: Yeah, that's not completely unique. 484 00:28:02,320 --> 00:28:07,440 Speaker 4: So there's also some parrot species to have about similar 485 00:28:07,480 --> 00:28:09,840 Speaker 4: distributions of actually left. 486 00:28:09,800 --> 00:28:13,000 Speaker 1: Clawdness really the way there are parents that skew the 487 00:28:13,080 --> 00:28:16,640 Speaker 1: other way. They're like ninety percent left handed, left clawed. 488 00:28:16,760 --> 00:28:21,000 Speaker 4: Yeah, left footed, claud whatever. There's a lot of research 489 00:28:21,000 --> 00:28:24,320 Speaker 4: coming from Australia on that. So if you look at birds, 490 00:28:24,680 --> 00:28:27,600 Speaker 4: a lot of birds don't do a lot of food 491 00:28:27,680 --> 00:28:33,200 Speaker 4: handling with their claws, So parrots actually are species that 492 00:28:33,359 --> 00:28:36,760 Speaker 4: do handle food and they also do other like a 493 00:28:36,760 --> 00:28:38,600 Speaker 4: little bit more complicated tasks. 494 00:28:40,280 --> 00:28:42,800 Speaker 1: Yes, it turns out humans are not the only animals 495 00:28:42,800 --> 00:28:46,760 Speaker 1: with handedness or a side preference. Lots of animals have it, 496 00:28:47,000 --> 00:28:50,280 Speaker 1: even down to flatworms which don't even have a brain. 497 00:28:50,920 --> 00:28:53,800 Speaker 1: But that still doesn't answer the question of why this 498 00:28:54,000 --> 00:28:58,320 Speaker 1: preference exists. Well, according to doctor Auglenburg, you might all 499 00:28:58,360 --> 00:29:00,400 Speaker 1: have to do with efficient See. 500 00:29:02,560 --> 00:29:03,719 Speaker 2: Why does this happen? 501 00:29:04,160 --> 00:29:06,960 Speaker 4: I think this is sort of like a way of 502 00:29:07,120 --> 00:29:11,400 Speaker 4: making our brains more efficient. Your brain is about two 503 00:29:11,480 --> 00:29:14,000 Speaker 4: percent or so, depending a little bit of my over 504 00:29:14,200 --> 00:29:17,720 Speaker 4: body weight, but it takes about twenty percent of all 505 00:29:17,760 --> 00:29:21,520 Speaker 4: the calories I'm taking in to keeping it working. And 506 00:29:21,560 --> 00:29:23,760 Speaker 4: so if you know the brain is the most energy 507 00:29:23,840 --> 00:29:26,680 Speaker 4: hungry organ in the body, then it makes a lot 508 00:29:26,680 --> 00:29:31,160 Speaker 4: of sense that you specialize that you have like networks 509 00:29:31,240 --> 00:29:33,520 Speaker 4: that are only on one side, because if you double them, 510 00:29:33,600 --> 00:29:37,480 Speaker 4: like for example, kidney or something, you would like increase 511 00:29:37,840 --> 00:29:41,240 Speaker 4: the energy amount the organism needs without having like a 512 00:29:41,440 --> 00:29:44,840 Speaker 4: direct gain in the situation. And the other thing is 513 00:29:44,960 --> 00:29:48,920 Speaker 4: also if you do not take some like measures to 514 00:29:49,200 --> 00:29:52,920 Speaker 4: make the brain efficient and as small as possible, at 515 00:29:52,920 --> 00:29:55,800 Speaker 4: some point, umes would have been like really large heads, 516 00:29:55,880 --> 00:29:59,560 Speaker 4: which would have all sorts of problems, for example, doing birth, 517 00:30:00,400 --> 00:30:03,600 Speaker 4: doing like everyday life. You don't want to have a 518 00:30:03,640 --> 00:30:05,360 Speaker 4: head like four times the size. 519 00:30:05,520 --> 00:30:08,840 Speaker 1: Right, if we hadn't specialized the hemispheres, you mean. 520 00:30:09,040 --> 00:30:11,720 Speaker 4: Yeah, So if you hadn't blessed the hemispheres and you 521 00:30:11,720 --> 00:30:14,800 Speaker 4: would double everything in the brain, you would have had 522 00:30:14,800 --> 00:30:17,160 Speaker 4: a much larger head. Right, So this would not be 523 00:30:17,280 --> 00:30:19,200 Speaker 4: good for a number of reasons. 524 00:30:20,360 --> 00:30:23,160 Speaker 1: All right, that makes sense. We didn't involve to be 525 00:30:23,240 --> 00:30:26,360 Speaker 1: ambidexrous because for the most part, we don't really need 526 00:30:26,480 --> 00:30:30,840 Speaker 1: two dexterus hands. It's more efficient to invest brain resources 527 00:30:30,880 --> 00:30:33,800 Speaker 1: into making one of your hands more skilled than the other, 528 00:30:34,200 --> 00:30:37,280 Speaker 1: because that's probably good enough for most tasks like using 529 00:30:37,360 --> 00:30:40,440 Speaker 1: a tool or picking apart some food. But that still 530 00:30:40,520 --> 00:30:44,320 Speaker 1: doesn't explain why humans are sort of unique having one 531 00:30:44,400 --> 00:30:47,040 Speaker 1: kind of hand inness be more common than the other. 532 00:30:47,560 --> 00:30:50,720 Speaker 1: As we mentioned before, most other animals have a nearly 533 00:30:50,880 --> 00:30:55,160 Speaker 1: equal split between right and left handers or powers, but 534 00:30:55,240 --> 00:30:58,640 Speaker 1: in humans, ninety percent of people are right handed. Why 535 00:30:58,720 --> 00:31:02,440 Speaker 1: is that well? One idea, according totor Oglnburg, is that 536 00:31:02,520 --> 00:31:05,720 Speaker 1: having most people need the same handed makes it easier 537 00:31:05,920 --> 00:31:07,200 Speaker 1: to teach each other. 538 00:31:08,280 --> 00:31:10,880 Speaker 4: And one of the ideas that it is just like 539 00:31:11,160 --> 00:31:15,280 Speaker 4: easier to learn like a complicated thing if you. 540 00:31:15,280 --> 00:31:18,360 Speaker 2: Don't have to like also mimor reverse it in your brain. 541 00:31:18,480 --> 00:31:21,000 Speaker 4: Right, So if you're right handed, it's easier to learn 542 00:31:21,400 --> 00:31:24,280 Speaker 4: writing from a right handed person because you can just 543 00:31:24,440 --> 00:31:25,240 Speaker 4: like copy what. 544 00:31:25,160 --> 00:31:28,240 Speaker 2: They're doing compared to a left handed person. 545 00:31:28,320 --> 00:31:32,800 Speaker 4: So this ease of training and highly complicated things is 546 00:31:32,840 --> 00:31:35,840 Speaker 4: something that is one of the hypothesis widest is such 547 00:31:35,880 --> 00:31:37,880 Speaker 4: a strong right sided preference. 548 00:31:38,120 --> 00:31:40,800 Speaker 1: I see and I read that there's something called the 549 00:31:40,880 --> 00:31:44,800 Speaker 1: fighting hypothesis related to sort of the evolution of handedness. 550 00:31:44,800 --> 00:31:45,440 Speaker 1: What does that mean? 551 00:31:45,920 --> 00:31:51,120 Speaker 4: So there is a hypothesis that tries to link handedness 552 00:31:51,160 --> 00:31:57,320 Speaker 4: directly to some sort of evolutionary survival fitness advantage. And 553 00:31:57,360 --> 00:32:01,400 Speaker 4: the idea behind this is that left handers have a 554 00:32:01,480 --> 00:32:06,000 Speaker 4: sort of like advantage in fighting in combat sports. It's 555 00:32:06,120 --> 00:32:08,800 Speaker 4: very well known and there's a lot of research paper 556 00:32:09,120 --> 00:32:12,920 Speaker 4: showing that. For example, I think like boxing, because a 557 00:32:12,960 --> 00:32:17,280 Speaker 4: lot of people that do fight they've been trained in 558 00:32:17,760 --> 00:32:20,880 Speaker 4: like fighting right handed opponents, which means that if you 559 00:32:20,960 --> 00:32:24,360 Speaker 4: face the left handed opponents and they're attacking from basically 560 00:32:24,360 --> 00:32:27,160 Speaker 4: the other side, you might have less experience in this 561 00:32:27,280 --> 00:32:30,400 Speaker 4: sort of combat situation, and then the left tender might 562 00:32:30,480 --> 00:32:34,680 Speaker 4: have a advantage. And this sort of like shows pretty 563 00:32:34,680 --> 00:32:37,760 Speaker 4: well if you look at the sports for things like, oh, 564 00:32:37,920 --> 00:32:42,160 Speaker 4: you call it like fencing. So the fighting advantage hypothesis 565 00:32:42,320 --> 00:32:47,360 Speaker 4: is that left handers may stay in the population because 566 00:32:47,720 --> 00:32:51,600 Speaker 4: they have a survival fitness advantage in fighting, but only 567 00:32:52,240 --> 00:32:54,720 Speaker 4: as long as they're rare. If there's a lot of 568 00:32:54,800 --> 00:32:57,920 Speaker 4: left handers there would be sort of like then destroying 569 00:32:57,920 --> 00:33:03,080 Speaker 4: the advantage because then they're not very surprising anymore. Right, right, 570 00:33:03,520 --> 00:33:06,800 Speaker 4: And it's a bit of an ongoing discussion whether you 571 00:33:06,880 --> 00:33:13,120 Speaker 4: can explain behavior like directly with these fitness advantages, because 572 00:33:13,440 --> 00:33:16,840 Speaker 4: I mean not sure how many fights you or your 573 00:33:17,000 --> 00:33:21,280 Speaker 4: ancestors ever got that had direct relevance for your survial. 574 00:33:22,160 --> 00:33:24,920 Speaker 4: So I would say it's a hypothesis. I would take 575 00:33:24,960 --> 00:33:26,000 Speaker 4: it with a grain of salt. 576 00:33:27,000 --> 00:33:29,560 Speaker 1: Okay, last question, anything else you think people should know 577 00:33:29,600 --> 00:33:31,360 Speaker 1: about left handedness. 578 00:33:31,680 --> 00:33:35,480 Speaker 4: I generally would say, your handedness is something that refers 579 00:33:35,520 --> 00:33:38,600 Speaker 4: to the motor cortex. And if you look at like 580 00:33:38,960 --> 00:33:44,000 Speaker 4: the largest meta studies integrating research over the last couple 581 00:33:44,080 --> 00:33:49,520 Speaker 4: decades as pretty convincing evidence that left handedness and intelligence 582 00:33:49,640 --> 00:33:52,760 Speaker 4: is not linked, so leatenders and right handers. 583 00:33:52,480 --> 00:33:56,400 Speaker 2: Seem to be equally smart and capable. 584 00:33:56,840 --> 00:34:00,120 Speaker 4: The same goes also for creativity, there was always this 585 00:34:00,200 --> 00:34:03,160 Speaker 4: idea left handers some more creative, and it's. 586 00:34:03,080 --> 00:34:04,680 Speaker 2: Quite interesting if you look at it. 587 00:34:04,840 --> 00:34:07,200 Speaker 4: If you ask left and right handed people whether they 588 00:34:07,280 --> 00:34:10,600 Speaker 4: believe left handers are more creative than right handers, is 589 00:34:10,640 --> 00:34:17,040 Speaker 4: a ginormously strong statistical effect. So everybody believes left hand 590 00:34:17,080 --> 00:34:18,920 Speaker 4: is some more creative than right handers. 591 00:34:18,960 --> 00:34:21,600 Speaker 2: And actually parents use this that advice. 592 00:34:21,800 --> 00:34:24,120 Speaker 4: Right, so you're really having a left handed child, you 593 00:34:24,200 --> 00:34:25,359 Speaker 4: tell him become an. 594 00:34:25,320 --> 00:34:28,440 Speaker 2: Artist or you become a rock star, whatever. 595 00:34:28,719 --> 00:34:32,239 Speaker 4: But if you actually have left handers right handers create art, 596 00:34:32,360 --> 00:34:35,719 Speaker 4: and then you take like artists who are experts in 597 00:34:35,840 --> 00:34:39,920 Speaker 4: this field and let them rate the products, there's absolutely 598 00:34:40,000 --> 00:34:43,879 Speaker 4: no difference. So I think in general you should think 599 00:34:43,920 --> 00:34:48,160 Speaker 4: of handedness and something that is referring to the motorabilities. 600 00:34:48,280 --> 00:34:51,120 Speaker 4: It's caused by the mortal cortex and does not have 601 00:34:51,520 --> 00:34:56,280 Speaker 4: any sort of strong effect on like how smart you are, creative, 602 00:34:56,400 --> 00:35:00,239 Speaker 4: you're any other like brain abilities, because it's just is 603 00:35:00,280 --> 00:35:04,080 Speaker 4: not affecting the brain networks that do these things. Anything 604 00:35:04,160 --> 00:35:07,799 Speaker 4: related to thinking or this idea there's sort of like 605 00:35:07,840 --> 00:35:10,960 Speaker 4: a coherent left handed personality. 606 00:35:11,120 --> 00:35:16,360 Speaker 2: They're rere spirited, creative thinkers and stuff like that. 607 00:35:16,360 --> 00:35:20,960 Speaker 4: That's just very like old ideas that did not hold 608 00:35:21,040 --> 00:35:21,799 Speaker 4: up very well. 609 00:35:22,160 --> 00:35:23,319 Speaker 2: Sorry, left handers. 610 00:35:23,480 --> 00:35:27,000 Speaker 1: So, left handers, is there anything else you think people 611 00:35:27,040 --> 00:35:30,600 Speaker 1: should know about left handedness or handedness in general. 612 00:35:31,200 --> 00:35:34,399 Speaker 3: Well, I think it's very important to look at left 613 00:35:34,400 --> 00:35:38,320 Speaker 3: handedness as a normal form of handedness. There's nothing abnormal 614 00:35:38,360 --> 00:35:41,600 Speaker 3: about it. They are just different in many ways. 615 00:35:41,840 --> 00:35:42,480 Speaker 2: So this is. 616 00:35:42,640 --> 00:35:46,440 Speaker 3: Really something that you cannot just change the handedness just 617 00:35:46,480 --> 00:35:47,560 Speaker 3: by writing with that hand. 618 00:35:47,840 --> 00:35:50,480 Speaker 1: I think you're saying that trying to switch someone doesn't 619 00:35:50,640 --> 00:35:54,160 Speaker 1: just automatically flip the brain. It's like you're really forcing 620 00:35:54,200 --> 00:35:57,200 Speaker 1: something that the brain is not predisposed to do. 621 00:35:57,520 --> 00:36:01,160 Speaker 3: Yes, that's well said. You know that's not anything. So 622 00:36:01,400 --> 00:36:04,560 Speaker 3: go to an occupation service, have been tested out and 623 00:36:04,600 --> 00:36:07,000 Speaker 3: make sure that the child writes with the right hand. 624 00:36:07,360 --> 00:36:09,720 Speaker 1: No, it was correct, yes, right, not the right hand, 625 00:36:09,760 --> 00:36:15,640 Speaker 1: the correct hand. That's funny, all right. Well, it sounds 626 00:36:15,680 --> 00:36:18,160 Speaker 1: like the question of why some people are left handed 627 00:36:18,400 --> 00:36:20,919 Speaker 1: is still a bit of a mystery. We know a lot, 628 00:36:20,960 --> 00:36:23,879 Speaker 1: but there's still a lot we don't know. I guess 629 00:36:23,920 --> 00:36:26,720 Speaker 1: we just need to wait for the right person to 630 00:36:26,760 --> 00:36:30,759 Speaker 1: figure out what's left. Hey, thanks for joining us. See 631 00:36:30,760 --> 00:36:36,960 Speaker 1: you next time. You've been listening to Science Stuff production 632 00:36:37,080 --> 00:36:41,560 Speaker 1: of iHeartRadio, written and produced by me or HM candidate 633 00:36:41,640 --> 00:36:45,640 Speaker 1: by Rose Seguda, executive producer Jerry Rowland, an audio engineer 634 00:36:45,640 --> 00:36:48,480 Speaker 1: and mixer Jacey Pecrom And you can follow me on 635 00:36:48,520 --> 00:36:51,759 Speaker 1: social media. Just search for PhD Comics and the name 636 00:36:51,800 --> 00:36:54,520 Speaker 1: of your favorite platform. Be sure to subscribe to sign 637 00:36:54,560 --> 00:36:57,520 Speaker 1: Stuff on the Arheart Radio app, Apple Podcasts, or wherever 638 00:36:57,719 --> 00:37:00,839 Speaker 1: you get your podcasts. Please tell your friend friends we'll 639 00:37:00,880 --> 00:37:12,440 Speaker 1: be back next Wednesday with another episode. Hey, please take 640 00:37:12,480 --> 00:37:15,640 Speaker 1: a second and leave us a review on Apple Podcasts, Spotify, 641 00:37:15,960 --> 00:37:18,839 Speaker 1: or wherever you listen to the podcast. Thanks a lot,