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Evolution spent nearly 400 million years crafting these works of art, two of the most important
pieces of the human evolutionary puzzle. Yet 99% of us end up being good with one hand
and not the other, for common tasks like writing, high-fiving, and the all-important one-handed
texting. Even life itself seems to have chosen sides:
our amino acids are said to be “left-handed”, our DNA turns in a right-handed helix.
Both hands seem fully capable, both are connected to fully functional arms, so we’d expect
an even split when it comes to which hand we prefer. In the animal kingdom, where we
find creatures with a preference for one paw, hoof, or wing, it’s usually 50/50. Yet on
average, only 1 out of 10 humans are southpaws. I guess the real question is “Why are so
few people left handed?”
Maybe because it's the world is conspiring against them…
Spiral notebooks. Scissors. E-readers. Video game controllers. Zippers. Even can openers.
If only someone would open a chain of stores specifically stocked with products for left-handers.
That's a money-maker.
Even language hates lefties. To be correct is to be right… and correct
is also word that comes from “right”. Gods are full of righteousness.To be skillful
is to have dexterity. Kings are regal. Left itself comes from Old English, meaning
“weak”. Words for left give us sinister. Gauche. Maladroit. Bad dancers have two left
feet.
But language turns out to be an important part of the puzzle.
Our brains are cross-wired, meaning the right hand is controlled by the left side, and vice
versa. But that doesn’t mean our brain’s symmetrical. In the 1860s, French scientist
Paul Broca discovered that a region of our brains used for speech processing is usually
located on one side. Language is a complex process, and the move to one hemisphere probably
helps the brain deal with it more efficiently.
Today we know that in 99% of right-handers’ brains, Broca’s area is located only in
the left hemisphere. And in left-handers’ brains… it’s also on the left, 70% of
the time. Only 19% of lefties process speech in the right hemisphere, and 20% of them use
both. So… language and hands, not directly linked.
That’s… confusing.
Two similar theories have been proposed to explain this. They suggest that as early humans
evolved, a gene mutant popped up that threw a whole BUNCH of of our brain’s functions
to one side and allowed them to specialize.
If you have two copies of the so-called Right Shift mutation, language and hand dominance
move to the left hemisphere. That shift is slightly less if you carry one copy, and if
you don’t carry the Right Shift mutation at all, language and handedness could go to
the right or left, just by chance.
This means instead of their being a gene for left-handedness, it’s really the lack of
a gene.
A genetic influence makes sense, since parents seem to sometimes pass on handedness to their
kids. While two right-handed parents only have a 9% chance of having a left-handed child,
one parent being left-handed raises that to 19%, and two to 26%.
But research has found evidence of right-hand preference in captive chimps, and yes, I’m
talking about throwing poop. This would mean that a brain shift for coordination came first,
before we became the talking, throwing geniuses we are today.
There’s even another theory, which goes back to the video we did on how our bodies
tell right from left when it comes to our guts, that this whole brain-hand sidedness
can be traced all the way back to our embryonic days. And in 2013, researchers reported that
some of the same genes that tell our spleens and stomachs which way is which are linked
to brain asymmetry.
I know you guys hate this, but the answer is we still don’t really know for sure why
more of us aren’t left handed. Sorry. As you’ve seen we’ve got some great ideas
that people are still researching, but that’s how science works!
Of course, if being right-handed and shifting our speech and coordination to one side was
such a great thing for evolution, then why do lefties still exist?
One idea says whether it’s on the baseball mound, the tennis court, we right-handers
do worse when facing lefties. We’re just not used to all your strange Southpaw ways.
If you happen to be holding a sword instead of a tennis racket, being a lefty might be
a great survival tool.
A simpler theory is just that nature enjoys variety. Chris McManus believes that left
handers may have what he calls “random cerebral variation”, their brains are more… shuffled
up. This might lead to more unexpected connections, more cross-talk between the right and left
hemispheres, and maybe more creativity. What’s clear is that having a diverse set of brains
have made humans a much more interesting species.
We may not have all the answers yet, but these questions have taught us a lot of important
lessons about the brain along the way. And hey, at least we’re not burning them at
the stake.
Stay curious.
If you want to learn more about southpaw science, check out the book "A Left Hand Turn Around
the World" by David Wolman, link down in the description.