Why is your dominant hand so much better at tasks like writing?

A new PNAS paper reframes the nature vs nurture debate: handedness preference is innate, present before birth, and that genetic bias becomes a big skill gap through decades of lopsided practice. 

Using 3D reaching tasks, researchers found little dominant advantage under a wrist weight, but a large one when using a stick-like tool the dominant arm has practiced with for life. When people learned to write with their elbow instead, a brand new effector, the advantage disappeared entirely. 

It's a clean example of how a small innate tendency snowballs into a large behavioral asymmetry; nature sets the starting point, experience does the rest. This was a collaboration between David Geffen School of Medicine at UCLA and The Johns Hopkins University School of Medicine. 

Read the entire paper: Arm dominance is an emergent effect of practice executing complex trajectory shapes required by tools and objects