The world is designed around our right-handedness.

From school desks to handshakes, life has adapted to fit the needs of the 90% of people who biologically identify as a “righty.” But the question of why the overwhelming majority of human cultures favor the right hand has long puzzled scientists seeking answers.

Despite decades of research, right-handedness has remained a mystery until now. A recent study from the University of Oxford reveals that this predisposed characteristic is actually a byproduct of how our brains formed, and more specifically, of learning to walk upright.

Archeologists have traced evidence of right-hand dominance back to the Neolithic era, but some argue it’s been true since even before then. The data revealed that handedness is rooted in specific brain regions around the time bipedalism emerged.

When humans began walking, their unusually strong preference for hand dominance differed from that of other primate species, which still show more ambiguous forms of ambidexterity.

For humans, hand preference begins in utero and continues to consolidate during adolescence. Despite the predisposition, scientists say environmental and developmental factors can play a role. But it’s almost a self-fulfilling prophecy that the more you defer to one hand or another, especially during early life, the more the body adapts and produces physical differences in bone shape, density, and strength.

Yet scientists still don’t fully understand why humans evolved such a strong bias toward one side, but the study reveals a major clue.

“This is the first study to test several of the major hypotheses for human handedness in a single framework,” researcher Dr. Thomas A. Püschel said in the study.

“Our results suggest it is probably tied to some of the key features that make us human, especially walking upright and the evolution of larger brains. By looking across many primate species, we can begin to understand which aspects of handedness are ancient and shared, and which are uniquely human.”

The study also reveals a correlation between smaller-brained, less upright primates and more flexible hand preference, compared to humans’ overwhelming dominance of one side.

At the same time, neuroscientists widely understand that engaging in daily activities with your non-dominant hand can temporarily force the brain to adapt and create new neural pathways through a process known as neuroplasticity.

Studies have shown that repeatedly practicing tasks with the opposite hand strengthens connections in regions associated with movement and coordination.

Researchers say that using the dominant hand vs. the non-dominant hand serves different neurological functions. The dominant hand tends to specialize in precision and fine motor control, and the non-dominant hand is often better at stabilization and support during movement— which makes sense if you’ve ever held your arm out to balance.

Though we’re getting closer to fully understanding the overwhelming right-hand dominance, the issue may still be more nuanced, especially given environmental factors at play.

As for lefties, they’ll likely continue doing what they’ve always done: figuring out how to survive in a world built opposite.