Why Do Humans More Often Use the Right Hand Than the Left?

Legendary musician Jimi Hendrix was renowned for his left-handed guitar playing. In fiction, Ned Flanders from The Simpsons even opened a Leftorium store dedicated to left-handers. Yet evidence shows that right-handedness is the most active, dominant hand for a large portion of Earth’s population.

A recent study published in the journal PLOS Biology has shed light on the evolutionary reasons behind this preference. The researchers analysed data from 2,025 primates across 41 species. They found that although spider monkeys and langurs show relatively high levels of lateralisation, this trait is far more extreme in humans.

Phylogenetically, humans are considered evolutionary outliers. Our extreme reliance on a single hand appears to diverge from other primates.

“However, this outlier status disappears when brain size (endocranial volume) and the intermembral index (the ratio of arm to leg length) are included in the analysis. This indicates that these factors lie at the heart of the emergence of handedness in humans,” the researchers write in their report, as cited by IFLScience.

Anatomically, the long human legs are closely tied to our ability to walk on two feet (bipedalism). This contrasts with brachiating apes that use their arms to swing through trees.

According to the study authors, when our ancestors began adopting upright walking, the upper limbs were automatically freed from their role as the primary mobility tool.

“This created new opportunities for tool use, gesture-based communication, and other fine-motor behaviours. In this context, having one hand more dominant provides a substantial performance advantage,” the researchers explained.

As humans stopped using hands for walking, they gained the opportunity to use their hands asymmetrically for a range of more complex functions.

At the same time, increases in brain size and cortical reorganisation drove hemispheric specialization. This enhanced neural efficiency to support those specialised motor behaviours, especially after the emergence of the genus Homo.

Using archaeological data on limb proportions and brain volume in ancient hominins, the researchers were able to simulate the strength of hand dominance in our extinct ancestors.