10% vs 90% :)

A photo showing raised human hands.

Tima Miroshnichenko/Pexels

Handedness, yours truly is a lefty, 90% of the human race are righties but it seems it's baked in:)

About nine out of every ten humans on Earth are righties. This strange imbalance stretches across cultures, continents, and history itself. No other primate species comes remotely close to showing such a strong population-wide preference. 

Now, a new study from researchers at the University of Oxford suggests the answer may lie in two evolutionary changes that transformed our species more than any others: walking upright and growing unusually large brains. 

The researchers propose a two-stage explanation for human handedness. First came bipedalism. As early human ancestors began walking upright, their hands were freed from locomotion. 

This likely created new evolutionary pressure for specialized hand use during tasks such as carrying objects, manipulating tools, or gesturing. The study found that locomotion strongly influences handedness patterns across primates. 

The second phase came later with brain expansion

Using evolutionary models, the researchers estimated handedness in extinct human relatives. Early hominins such as Ardipithecus and Australopithecus likely had weak right-hand preferences similar to modern apes. 

However, the bias strengthened in species such as Homo erectus and Neanderthals before reaching its modern extreme in Homo sapiens. “It is with the emergence of the genus Homo, and particularly the onset of significant encephalization, that we observe a marked increase in MHI values,” the study authors added.

The significance of these findings

The study suggests human right-handedness may be deeply rooted in the same evolutionary changes that transformed how our ancestors moved and interacted with the world. 

However, some important questions remain unanswered. For instance, scientists still do not know why left-handedness survived throughout human evolution, or how much human culture helped strengthen right-hand dominance over time.

The study is published in the journal PLOS Biology.

But thereare other variables. Chirality and the handedness of the weak nuclear force
as it only works left handed. So does life. 

Two enantiomers of a generic amino acid that is chiral

Scaling it up ...

The Primitive Node ...

The initial stages of human embryonic development (embryogenesis)

How the Node Breaks Symmetry

The connection between the node and "left-handedness" relates to embryonic left-right asymmetry (how our internal organs are arranged) rather than hand preference.

• Nodal Flow: The ventral surface of the node contains hundreds of microscopic, rotating hairs called cilia. These cilia tilt and spin in a specific clockwise rotation, creating a leftward flow of extracellular fluid. This fluid movement pushes signaling molecules to the left side of the embryo.
• Gene Activation: This leftward flow triggers the localized expression of specific genes—most notably the Nodal gene and the Pitx2 transcription factor—strictly on the left side.
• Biological Outcomes: This chain reaction dictates that the heart, liver, and other asymmetrical organs develop in their proper anatomical positions.

In essence ...

Embryonic asymmetry: The left side gets all the best genes

This is why lefties like yours truly are still around. :)