[MUSIC] [MUSIC] 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.
