Mostly Right-Handed Humans, Why?

Imagine a Neanderthal, picture them hunched over, scraping an animal hide with a stone tool. They grip the hide between their teeth, stretching it taut. Suddenly, the tool slips, leaving a nasty scratch across their front tooth. This wasn't uncommon – these tiny scratches hold a big clue about our ancestors!

Fast forward to today, scientists have analyzed these scratches on teeth from various sites. It turns out, that most Neanderthals, just like us, were right-handed. Shocking, right? Here's the kicker: no other mammal, not even our closest primate relatives, shows this one-handed preference. Even stranger, no human population has ever been mostly left-handed.

So, what's the deal with our right-handed obsession? It all boils down to some unique traits that set us apart from our chimpanzee cousins: walking upright and, you guessed it, making tools.

Being right-handed might be deeply rooted in our evolutionary history. But lefties have their perks too! Here's the thing: handedness isn't a simple on/off switch. Some people are strongly right or left-handed, while others fall in between. We use our hands for everything, from delicate tasks like threading a needle to gripping a carrot while chopping it (lefty here, holding the carrot!).

Now, get this: each of our hands is controlled by the opposite side of the brain. The left hemisphere controls the right side of the body, and vice versa. These hemispheres aren't identical twins, leading to different functions happening in different brain areas. This separation, called lateralization, is pretty extreme in humans compared to other creatures. This might explain why we eventually favored one hand over the other.

Think about it: 99% of people have a dominant hand, and evidence suggests this has been the case for a long time. Cave paintings from around the world depict animals, hunting scenes, and a surprising number of human hands. Interestingly, most of these hand stencils are left-handed! This suggests the artists, likely right-handed, placed their left hand on the cave wall and blew pigment over it.

Hand preference can even be seen in skeletons, especially in athletes who favor one arm more. Their dominant arm bone becomes thicker from repeated stress. We might be the only species with such a strong hand dominance, but evidence suggests our extinct hominin relatives (think Neanderthals) were mostly right-handed too.

The coolest clue comes from...teeth! Scientists suspected Neanderthals were right-handed based on their arm bones. But, finding complete hominin fossils with both arms preserved is rare. So, when researchers spotted tiny tool-induced scratches on Neanderthal teeth, similar to that of Croatian cave dwellers, a light bulb went off.

These scratches revealed two things: how far back we can trace handedness and what behaviors might be linked to it. Back then, our ancestors used their teeth like a third hand. Imagine pulling a hide taut with your front teeth and left hand, scraping it with a tool in your right. If you slipped, the scratch would run diagonally across your teeth. The direction of the scratch reveals which hand held the tool.

Similar scratches were found on 500,000-year-old teeth from Spain and even on a 1.8-million-year-old Homo habilis tooth from Tanzania! While one right-handed Homo habilis doesn't prove the whole species was right-handed, it shows handedness is an ancient trait. Since no other primates favor one hand so much, this must have developed after our split from chimps.

But why did multiple hominin species develop hand preference? And why the right hand? The search for a "handedness gene" is ongoing. Studies show some heritability and a higher frequency of left-handedness in men, but no single gene is responsible. It seems several genes have minor effects, and other factors are at play.

Some scientists point to brain lateralization and tool use. Brain scans show a specific region in the left hemisphere plays a key role in manipulating objects, including tools. Since the left hemisphere controls the right hand, the development of tools millions of years ago might have favored the right hand over time. Interestingly, bipedalism might also be linked to hand preference. Some bipedal mammals like kangaroos (though mostly left-handed and not tool users) show a preference for one hand.

So, if being right-handed is linked to tools and the left hemisphere, why are there still lefties? Here's a theory: everyone might have been right-handed after the development of stone tools. Lefties might have emerged later due to genetic mutations. Since lefties are a minority in our right-handed world, there must be an evolutionary advantage.

Here's where it gets interesting: lefties tend to have less lateralized brains, and process information more evenly across both hemispheres. This can involve better communication, memory, and language skills. Lefties also have an incredible edge – in physical combat!

Think of it as a boxing match. You are a right-hander facing right-handed only opponents. You expect a kick from their right side. But a left-handed opponent throws jabs from unexpected places, giving them an advantage. This "left side advantage" is seen in contact games but not in non-contact games like archery. Studies also show that left-handed boxers and fighters tend to win! This advantage may directly increase left hemisphere survival.

It could also explain that the left is a minority. If more people were left-handed, the surprise advantage would disappear.

So, there you have it! Right-handedness seems deeply rooted in our evolutionary history, tied to our specific brains and tool use. While the precise origin of right-handedness remains a mystery, there may be enough evolutionary advantages for left-handedness to survive. After all, it just shows the incredible diversity that makes us human – there is no one "right" way to do it!