Why are some people left-handed? – Daniel M. Abrams
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Why are some people left-handed? – Daniel M. Abrams


If you know an older left-handed person, chances are they had to learn to write
or eat with their right hand. And in many parts of the world, it’s still common practice to force
children to use their “proper” hand. Even the word for right
also means correct or good, not just in English,
but many other languages, too. But if being left-handed is so wrong, then why does it happen
in the first place? Today, about 1/10 of the world’s
population are left-handed. Archeological evidence shows
that it’s been that way for as long as 500,000 years, with about 10% of human remains showing the associated differences
in arm length and bone density, and some ancient tools and artifacts
showing evidence of left-hand use. And despite what many may think,
handedness is not a choice. It can be predicted even before birth
based on the fetus’ position in the womb. So, if handedness is inborn,
does that mean it’s genetic? Well, yes and no. Identical twins, who have the same genes,
can have different dominant hands. In fact, this happens as often as it does
with any other sibling pair. But the chances of being
right or left-handed are determined by the handedness
of your parents in surprisingly consistent ratios. If your father was left-handed
but your mother was right-handed, you have a 17% chance
of being born left-handed, while two righties will have
a left-handed child only 10% of the time. Handedness seems to be determined
by a roll of the dice, but the odds are set by your genes. All of this implies there’s a reason that evolution has produced
this small proportion of lefties, and maintained it
over the course of millennia. And while there have been several theories attempting to explain why handedness
exists in the first place, or why most people are right-handed, a recent mathematical model suggests that the actual ratio
reflects a balance between competitive and cooperative
pressures on human evolution. The benefits of being left-handed are clearest in activities
involving an opponent, like combat or competitive sports. For example, about 50% of top hitters
in baseball have been left-handed. Why? Think of it as a surprise advantage. Because lefties are a minority
to begin with, both right-handed
and left-handed competitors will spend most of their time
encountering and practicing against righties. So when the two face each other, the left-hander will be better prepared
against this right-handed opponent, while the righty will be thrown off. This fighting hypothesis, where an imbalance in the population results in an advantage for left-handed
fighters or athletes, is an example of negative
frequency-dependent selection. But according to the principles
of evolution, groups that have a relative advantage tend to grow until
that advantage disappears. If people were only fighting and competing
throughout human evolution, natural selection would lead to more
lefties being the ones that made it until there were so many of them, that it was no longer a rare asset. So in a purely competitive world, 50% of the population
would be left-handed. But human evolution has been shaped
by cooperation, as well as competition. And cooperative pressure pushes handedness distribution
in the opposite direction. In golf, where performance
doesn’t depend on the opponent, only 4% of top players are left-handed, an example of the wider phenomenon
of tool sharing. Just as young potential golfers can more easily find
a set of right-handed clubs, many of the important instruments
that have shaped society were designed for
the right-handed majority. Because lefties are worse
at using these tools, and suffer from higher accident rates, they would be less successful
in a purely cooperative world, eventually disappearing
from the population. So by correctly predicting
the distribution of left-handed people
in the general population, as well as matching data
from various sports, the model indicates that the persistence of lefties
as a small but stable minority reflects an equilibrium that comes from competitive
and cooperative effects playing out simultaneously over time. And the most intriguing thing is what the numbers can tell us
about various populations. From the skewed distribution of pawedness
in cooperative animals, to the slightly larger
percentage of lefties in competitive hunter-gatherer societies, we may even find that the answers
to some puzzles of early human evolution are already in our hands.

About James Carlton

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100 thoughts on “Why are some people left-handed? – Daniel M. Abrams

  1. I feel bad for the right handed people who have to suffer being seated on a seat for right handed people. You know what kind of seat I'm talking about, right?

  2. I'm right handed, but after a lot of practice I can use my left hand too, I'LL NEVER HAVE MY ARM ON THE RINGS FROM A SPIRAL NOTEBOOK AGAIN

  3. I’m right handed but i eat my food “wrong”. I hold my knife and fork opposite of what’s “right” which is weird.

  4. I always wonder why people go "ur a leftie?!" When they see me writing with my left hand but i guess it works out cuz im ambidextrous 🤷‍♀️ so i love to just say "no" and nothing else

  5. me and my twin sister: write
    people: omg you write with different hands you're right and you're left… You must have had trouble with writing all your life since you're left and that's hard! This explains EveRyThiNg!

    Also I've been forced to write with my right hand once or twice by my teachers at primary school but they soon gave up. What's all that rubbish about anyway? If you write with left it's not as though you continually touch the paper with the back of your hand, dragging your hand over the paper, smudging all the ink… I mean, some people do, but I don't. Ot's not as though right handed people do the same backwards, dragging THEIR hand over the paper… right?

  6. I think my school has broken a record for most left handed people in one school… seriously I think almost half of the students and teachers are left handed

  7. i’m a lefty but my family always told me to eat with right hand so many times i became used to it. Also for some reason i can draw in computers with mouse and the result is like what i usually draw with hands. well, guess im ambidextrous..

  8. Oof both my parents are right handed but here I am left handed but my grandmother and uncle are left handed, out of my class of 76 there’s only 2 lefties! also in my city lefties were valued by the vikings as they were able to swing a sword better 🤔

  9. I’m right handed. But I can write on a chalk board with either hand and the text looks identical. I also bowl left handed rather than right.

  10. As a left handed person- I’m getting pretty annoyed by the amount of left handed people in this comment section just talking about problems that I’m already aware of.

  11. This is really crazy because my mother is right handed, my father is left handed. Both me and my sibling are mixed handed. (NOT AMBIDEXTROUS). And I just realized everything I do left handed would fall into the "competition" category (I'm left handed at baseball, fighting, holding things like brooms and sticks etc) and right handed at everything involving tools (writing, cutting, actual tools, etc). Wild

  12. I was actually going to be left handed I would pick up stuff with my left hand and my dad wanted me to be righted handed so he would take it off me and helped me pick it up with my right hand and now I am right handed 😅😂❤️

  13. Im a leftie im friends with righties so its ok if ur one of the two it dosent matter if ur a lefty or a rightie you were born like that plus your a beutiful person!

  14. Perhaps the origins of this has to do with the polar electromagnetic effect of the Earth. Left for Northern humanoids right for Southern. It also can be an indication that humans are a result of cross breeding of different species.

    It's could get really competitive to eat in winter months, in the ,north, if you didn't spend the whole summer farming.

  15. My friend's cat is "right handed", but was born without that paw, so she usually nubs stuff before giving her left paw a try at it, so if it's genetic, that makes a little more sense why she's so goofy

  16. My mom is ambidextrous because she wasn’t allowed to use her left hand. They claim to “even out the brain”. Wtf? Lol 😑
    Left handers are smart, I am proud of being a lefty!

  17. What about people who are ambidextrous? I always thought I was a right handed person, until I got my first job and realised other people can't switch hands when using power tools…

  18. Im a lefty and was forced to learn how to make nigiri in right as no one can teach me how to do it on left haaha man sometimes being a lefty is really challenging. But hey its part of the fun LMAO

  19. Both of my parents are right handed, almost every person in my family is right handed, BUT WHAT DO YOU KNOW, IM LEFT!😅

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