Why Do Humans Have a Right Hand More Often? The Trace Is in the Ancestor Who Walked Upright

JAKARTA - Around 90 percent of humans in various cultures use their right hand more often. The question is simple, why is the right hand so dominant, while the left hand remains a minority?

According to a report by The Independent, quoted on Friday, May 22, a new study published in the journal PLOS Biology says that the tendency is likely to start to be strong when human ancestors walk upright on two legs and their brains develop larger.

"Our findings suggest this may be related to the important features that make us human, especially upright walking and the evolution of a larger brain," said Thomas Püschel, one of the study's authors from the University of Oxford.

Scientists examined data on 2,025 individuals from 41 monkey and ape species. They tested various factors, ranging from tool use, food, habitat, body size, social life, brain size, to how they move.

The results showed that the two most powerful factors were brain size and the ratio of arm to leg length. This ratio is used by scientists to see the ability to walk on two legs.

With these two clues, researchers estimate the hand inclination of extinct human ancestors.

Early ancestors such as Ardipithecus and Australopithecus are thought to have had a slight tendency to use their right hand, similar to modern great apes. Both are early groups of ancient humans who lived millions of years ago in Africa and had begun walking on two legs.

The dominance of the right hand then seemed to be stronger in the genus Homo, which is the group of ancient humans in the evolutionary line of modern humans. This group includes Homo ergaster, Homo erectus, and Neanderthal, ancient humans who lived before modern humans.

The peak is seen in Homo sapiens, modern humans today.

There is one interesting exception. Homo floresiensis, a small-bodied and small-brained ancient human from Indonesia often dubbed "hobbit". This species is thought to have a tendency to have weaker hands. That goes hand in hand with its body adapted to walk upright as well as climb.

Scientists suspect that upright walking came first. When the hands are no longer used to move, the hands are free to carry, hold, and wear objects.

The bigger brain then strengthens the pattern. As the brain grows and reorganizes, the right-handed tendency becomes more established until it becomes the dominant pattern in modern humans.

"This is the first study to test several key hypotheses about human hand tendencies in one framework," said Püschel.

According to Püschel, comparisons of many primate species help scientists see which traits are old and inherited together, and which are human-specific.

The researchers next want to study the role of culture in maintaining right-handed dominance in various populations. They also want to answer the remaining questions, why left-handed humans still survive.