Why is almost everyone right-handed? A new study connects it to bipedalism
ox.ac.uk78 points by gmays 9 hours ago
78 points by gmays 9 hours ago
I always faced left when riding a skateboard back in the day, otherwise known in skater parlance as being "goofy-footed". Facing right felt as difficult as writing with my left hand. I always wondered whether that was just the way I first rode a skateboard and it stuck, but if that was the case, I would expect the distribution of which skateboarders face which way to be about even. But goofy-footed riders are in the minority. I'm right-handed as well. I wonder what's up with that.
I overused my right hand with computers - mouse + many keyboard keys like arrows, enter, backspace, etc
so I switched to a left-handed mouse. I cursed for about a week, then sometimes fumbled, and then it just worked.
Now years later, if I use a right-handed mouse to do say a first-person-shooter, I overcorrect like I'm drunk on wildly pitching ship.
left-hand is dialed in and precise.
I think some of this stuff is learned and not innate.
but yeah, goofy-foot on skateboard feels... just wrong.
I'm right-handed, but I snowboard goofy. Coincidence (or not?) my left leg is dominant. I can kick a ball just fine with my left foot, but when I try to kick with my right foot I feel like I'm going to capsize. When I'm riding a bike and I have to stop, my right foot goes down. When I start again I use my left leg to muscle the crank through the first revolution or two.
I think this is probably related to which eye is more dominant for you. I've never skateboarded, but if I imagine myself doing it, it would also be facing left. And it's because my right eye is dominant and I would like that to be facing forward.
Interesting. Never really thought about one of my eyes being dominant. I do have a bad habit of covering my left eye when reading in bed.
Quick test to find out which is pick a point in the distance, make a triangle with thumbs and fingers to look through, and slowly bring it toward your face. Wherever it ends up is your dominant eye.
Me too, but on a snowboard. (I suppose I'd be the same on a skateboard) My second time snowboarding was quite a few years after my first, and I just could not get the hang of it, wondering how I was faring so much worse than before. It took me all day to remember I was "goofy", and once I switched it was much better.
Yeah, I went snowboarding once in my life (loved it but it was exhausting) and naturally rode goofy-footed. They only thing I really needed to learn was slowing myself down.
I think skate stance is much more evenly distributed (closer to 50/50) than handedness (about 10% left).
Citation needed
"Of the 4,000 skaters in the Skatepark of Tampa Database, about half are goofy (44%) and half are regular (56%). But this near equality between skate stances doesn’t align with statistics on handedness. According to Scientific American, 90% of people are right-handed." ¹
"Out of the 610 professional skateboarders, 291 ride regular and 329 ride goofy. This means that 53% of skateboarders ride goofy and 47% ride regular! Way more skateboarders than expected ride goofy." ²
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¹ Dobija-Nootens, N., & Harrison-Caldwell, M. (2017, October 12). What determines your skate stance? Jenkem Magazine. https://www.jenkemmag.com/home/2017/10/12/determines-skate-s...
² Bande-Ali, A. (2024, August 25). Skateboarding: How many people ride goofy? Azeem Bande-Ali. https://azeemba.com/posts/skateboarding-how-many-people-ride...
What does "face left" mean? Left foot front? That's regular.
When I stand on a skateboard, both feet on, I face to the left. My right foot is in front, which I steer with while pushing myself with my left foot.
The article didn't really help me understand what it was about bipedalism that resulted in a right handed preference. Also in my family left hand dominates, we are a cluster of left handed people. My theory is if any child wants help with fine motor control the help is provided by a left hand to a left hand.
Oddly enough, a lot of my "nerd friends" are left handed, and I'm also left handed. /shrug
The original paper is titled "Bipedalism and brain expansion explain human handedness". It doesn't seek to explain why we have a right-handed preference specifically (vs left-handed), but rather why humans have such a strong handedness preference compared to ancestors who had only a mild right-handed preference.
IOW, why handed vs ambidextrous, not so much why left-handed vs right-handed.
> why handed vs ambidextrous
Did it even explain that? I'm ambidextrous, I have no handedness bias, so whichever I pick up to first learn something is the hand I use. So I'm a mix of left-handed and right-handed depending on the task. And yet I didn't really understand why that's odd because of my bipedalism?
without reading .. my immediate guess is that one hand is needed for maintaining upright balance, while the other hand grasps something important ?
I almost never see people using a left hand mouse these days.
As younger people start using computers they generally will learn with right-handed mice and will thus develop those fine motor skills in that hand. I wonder if this will make right-handedness even more dominant.
I mouse right-handed because it’s convenient, but I still naturally default to doing any novel task left-handed. It’s not a matter of fine motor skills, you can learn to do anything with either hand if you decide to, it’s just an unconscious preference.
With modern controllers the main joystick/thumbstick is on the left side. People are using both hands for fine control in different circumstances.
I wish they'd look into footedness as well and if there is some kind of correlation. Like orthodox vs southpaw in combat sports, goofy vs regular in skateboard, or just simply left vs right in football (soccer)
So why are us southpaws a rarity? The article and the linked research paper both point to bipedalism and bigger brains as the cause, and the paper vaguely seems to hint at selective pressures leading to the right hand getting favoured by the majority of the population, but why?
The question from the headline is excellent, if only it was actually answered.
Here's my five minute lunchtime hypothesis: it's because the heart is on the left. As human behavior demanded increasing precision from the hands, being a little farther from the heartbeat was a slight advantage.
That's a long time hypothesis of mine as well, but I think it stems from being stung or bitten by venom. If venom is injected into the bloodstream, it is desirable to be injected as far away from the heart as possible.
Some centimeters might not sound much, but over millions of years, the cumulative effect might be that 1% of human population every 10.000 years gets genetically optimized to hold their heart at a more protective spot.
Interesting!
Handedness is probably not (often) captured in healthcare records, but I'm wondering if epidemiologists could mine insurance claims (or some other data rich resource) to see if there's a correlation with serious outcomes (death, hospitalization, etc.) from venom and handedness.
That's a good idea, a very good idea actually, but I wonder about it's effectiveness due to a very small total number of snake bites nowadays, compared to the past.
Hundreds of thousands years in the past, hominids lived into much more tropical areas than today and there are a lot more spiders, scorpions, lizards and snakes in these warm places. It makes sense that insects and especially reptiles pushed the evolution of mammals in certain directions and the positioning of the heart in the human body might be one of them.
Today people live a much different lifestyle than having to deal with insects and reptiles all day long. I don't know if it is possible to decipher the past from today's data.
Wikipedia on Situs Inversus (visceral organs are mirrored, heart on the right, liver on left) [0], mentions mixed results regarding handedness. There would be a load of other confounding factors here and I know nothing about medicine.
Childhood handedness development within the brain became independent of organ positioning, after positioning had become established.
Situs inversus ("dextrocardia") is a rare disorder. What I postulated is a (very) small selective advantage leading to a neurological mechanism evolving over generations, not a direct line from the heart to handedness during development. Anyway, the effect would be very slight, and even if it did exist, it could have gone away later, but dexterity would have been baked in at that point (see also the ocular blind spot).
If this was the case wouldn't it be easier to measure the pulse in peoples left wrists? Which doesn't seem to be a thing?
Here’s my multiple years of anatomy classes response: the heart isn’t on the left. The aorta is, sure, but the vena cava is on the right. Also people with situs inversus (essentially all organs flipped laterally from “normal”) aren’t obviously more prone to left-handedness.
> Also people with situs inversus (essentially all organs flipped laterally from “normal”) aren’t obviously more prone to left-handedness.
I feel like this isn’t really an argument against the theory. If right handedness did evolve because of heart position, a later genetic mutation to have the heart on the opposite side wouldn’t suddenly undo the previous evolution towards right handedness.
Why are you assuming situs inversus, which occurs in species with no handedness (or, indeed, hands) came after handedness?
The argument is that the selection bias was towards precision and the hypothesis was that precision is influenced by heart position (which is, still, in the middle in humans)… individuals with situs inversus would be more precise in the left hand, thus if the causal hypothesis is correct AND the argument holds then there should be a selection bias that would result in a correlation between situs inversus presence and left-handedness.
In the end I don’t believe either the argument or the hypothesis hold even as much water as I can in either hand.
It might be hard to eliminate confounding factors depending on when the research was done. A lot of people in my generation were still dissuaded pretty heavily from writing with their left hands. I'm not entirely convinced anymore as a lay person that "handedness" is a real, distinct phenomenon that's primarily genetically determined or a result of the organization of the brain. It's equally possible that it's a learned preference and that the way the brain organizes around it is as a result of the preference's impact on how you have to solve problems with your preferred hand in a society that preferences right-handedness.
Not disagreeing that handedness is probably unrelated to heart position.
But why would situs inversus somehow be tied to this at all? If there's a gene that favors right-handedness, it's not like it would somehow "choose" left-handedness because the individual has their internal organs flipped.
Genes don’t favor (or not favor), but if a natural selection bias for precise dexterity exists AND heart lateral orientation affects dexterity precision THEN those with flipped lateral orientation should exhibit more dexterity in the left hand, thus they should be naturally selected for because of the same bias.
Now, I’d seriously doubt there’s any evidence whatsoever for the assumed selection bias in the first place, never mind any causal relationship between fine motor control and heart asymmetry, but the selection bias should apply to both flips of the anatomical mirror.
>Here’s my multiple years of anatomy classes response: the heart isn’t on the left.
Why is the left lung smaller, then?
not only smaller but having 2 lobes rather than 3, the left lung is possessed of a featureknown as the cardiac "notch" an involution of the lobe that corresponds to the larger left ventricle of the heart.
More piping to and from the heart exists on the left instead of the right?
the Aorta and Vena Cava are muchmore central than sinistral.
the aortic arch begins decent left of the coronary corpus, but becomes centralized, tandem with the Vena Cava.
The heart is asymmetrical, but it’s in roughly the center of the chest. The left auricle and ventricle are larger muscles because they’re pumping through the descending aorta to the extremities, that’s the systemic circulatory branch, the plumbing for which is also largely to the right, while the right are pumping into the lungs alone as part of the pulmonary circulatory branch. The left lung (right on those with situs inversus) has two lobes and basically accommodates the extra muscle mass on its side of the heart, but if you really want to kill someone you stab them through the sternum, kind of dead center, not where they hold their hand when performing patriotism.
>if you really want to kill someone you stab them through the sternum, kind of dead center, not where they hold their hand when performing patriotism.
Noted, thanks.
even this is wrong, a penetrating weapon aimed for the heart is applied below the sternum at roughly the positionof the 3rd shirt button, and thrust upward at shallow angle topass behind the manubrium, and is then levered into a pommel upward position so as to lacerate the heart
First, that’s because you want to keep your weapon, which implies you don’t really want to kill the killee. I’m assuming a half inch drill, and I’m leaving it powered up and spinning.
Second, note that what you don’t do when trying to hit the heart is aim left.
Well, yes, the point of the solid bone plate right in front of your heart is to block stabbings. And it works!
If you had a weapon that wasn't bothered by the presence of the sternum, and you wanted to stab the heart, you'd go right through the sternum.
the risk is one of being unable to extract the weapon expediently.
there is an unacceptable risk of having to abandon it.