World’s first right-hander could be this 550 million-year-old worm

As anyone who’s grown up favoring their southpaw can attest, the world overwhelmingly caters to right-handers. The vast majority of humans (somewhere around 85-90 percent) are right-handed, a tendency influenced by a combination of genes and environment. But it turns out this long-known preference towards the right may go back much further than scientists once thought, hundreds of millions of years further back, in fact. This preference toward the right may have been shared by some of the oldest known multicellular organisms.

That’s the core argument presented in a study published this week in the journal Scientific Reports. The international team of researchers examined over 100 well-preserved fossils of Spriggina floundersi, an ancient, inch-long worm-like animal that wriggled its way around southern Australia about 550 million years ago. The majority of those fossils shared something in common: they all showed the creature favoring its left side. And since fossils are mirror-image impressions captured at a moment in time, that actually means the animals favored their right side during life.

Researchers say this represents the earliest known example of this type of asymmetry in nature, and it may lend credence to the idea that handedness is hardwired deep into the evolutionary history of complex living creatures.

“The dominance of bends to the left in fossils of Spriggina suggests a preference for right turns in life and represents the oldest evidence of behavioural handedness among animals,” researchers write in the paper.

Evidence of ancient handedness, trapped in stone

Spriggina fossils date back to the Ediacaran Period, an era of immense biological change and adaptation. This period was responsible for introducing the first multicellular animals visible to the naked eye. Though they might not seem like much today, Spriggina and its contemporaries were some of the first animals capable of movement and other abilities scientifically considered complex behaviors. These are among the first organisms many people would identify as actual animals, rather than simply globs of goop.

The Spriggina fossil analyses in the study primarily came from Nilpena Ediacara National Park, located on the western part of the Flinders Ranges in southern Australia. It’s a remote area home to some of the best-preserved fossils from the Ediacaran Period. In this case, the collection of Spriggina fossils was buried together during some storm event around 550 million years ago.

Bend angles observed for Spriggina. Image: Scott D. Evans, Jenson Webb, Ian V. Hughes, William Parker & Mary L. Droser

And while it might not seem like it, the ancient hammerheaded worm has some key things in common with humans. Specifically, it’s among the earliest known examples of an animal with bilateral symmetry, meaning it has a distinguishable front and back, left and right, and top and bottom. That’s also true for humans and most animals today, but that wasn’t always the case. The findings suggest that favoring one side or the other isn’t some recent adaptation humans developed, but instead is possibly something deeply rooted in the way complex animals have evolved. While interesting on its own, the research stops short of answering why that’s the case.

“When we talk about being right-or-left-handed, most people likely think about how they hold a pencil or a kick a soccer ball,” American Museum of Natural History assistant curator of invertebrate paleontology and study lead author Scott Evans said in a statement. “But our research shows that an animal without hands or feet, living over 500 million years ago, may have had its own version of handedness.”

Humans and handedness: It’s in the genes

The fact that the overwhelming majority of humans today are right-handed isn’t entirely explained by genetics. Certain cultures in Asia and Africa have traditionally viewed left handedness as unclean. Others have gone even further, baselessly suggesting it was a sign of influence from satanic forces. Those and other cultural forces have led generations of people who naturally favor their left hand to be forcibly steered away from it. Tools and basic infrastructure are also largely designed around right-handedness, which can further pressure those who are naturally inclined to favor their left to conform to the social standard.

Related: [Why are most people right-handed?]

But still, even when accounting for those factors, handedness has a strong genetic component. Studies show that as many as 40 genes may play some role in determining handedness, which can present itself even before birth, in fetuses. Though it’s still not entirely certain what causes some people to favor the left hand, some researchers attribute it to random mutations during early brain development.

And while left-handers have typically had to work harder in many respects, their minority status does offer some unique advantages, especially in combat and sports. In fact, some modern athletes today, like tennis legend Rafael Nadal, were actually born favoring their right hand but trained to use their left specifically for the slight edge it offers.

Obviously, quite a few things happened in the 548 million years between Spriggina and the first human ancestors, which may account for right handed dominance today. Still, the findings suggest this ancient biological bias may have an origin story far older than anyone had expected.

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