La Jornada: Larger brains inclined 90% of humans to be right-handed

A new study reveals that about 90 percent of humans across cultures prefer to use their right hand to perform tasks, and this right-hand dominance may have started when early human ancestors began walking on two legs.

Decades of research on handedness in different species have revealed that no other primate species showed a population-level preference of this magnitude.

Genes, the brain, and the process of developing the body from the womb appear to work together to contribute to handedness.

But exactly why humans ended up being mostly right-handed remains an enigma, until now.

Now, a new study suggests that this trait emerged around the time when early human ancestors began walking upright and their brains began to increase in size.

“Our results suggest that it is probably related to some of the key characteristics that make us human, especially upright posture and the evolution of larger brains,” said Thomas Püschel, one of the authors of the study published in the journal PLOS Biology.

For the research, scientists analyzed data from 2,025 individuals belonging to 41 species of monkeys and apes.

Among these species, the researchers tested which of the main existing hypotheses best explained how laterality evolved, including tool use, diet, habitat, body mass, social organization, brain size and locomotion.

The scientists found the best theory to explain handedness when they took into account a large brain and the relative length of the arms compared to the legs, a standard anatomical marker of bipedal movement.

Using these two traits, researchers could also estimate the likely laterality of extinct human ancestors.

They discovered that early human ancestors, such as Ardipithecus y Australopithecusthey might also have had a slight preference for turning right, similar to that of modern great apes.

But right-hand preference appears to be becoming more prominent in the gender Homoincluding homo ergaster, The man stood up and the Neanderthals, reaching their modern extreme in A wise manwith the exception of Homo floresiensis.

This kind of hobbit small-brained, originally from Indonesia, appears to have had a lower preference for one hand, which fits with the general pattern that floresiensis It had a small brain and a body adapted to a combination of walking upright and climbing.

Scientists now suspect that bipedality arose first, allowing our ancestors to free their hands from the task of locomotion.

By having their hands free for other tasks, ancestors who used them for manual activities were favored by evolution.

The larger brains emerged later, and as they grew and reorganized, the rightward bias solidified into the nearly universal pattern seen today, the researchers say.

“This is the first study to test several of the main hypotheses about human handedness in a single theoretical framework,” said Dr. Püschel, an anthropologist at the University of Oxford.