Why Did Evolution Make Most Of Us Right Handed?

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Being Right-Handed Is Driven By Our Bipedal Stance…Here’s Why. There’s a reason why lefties are so valuable in baseball. Around 85% of us prefer our right hands to our left for both eating and writing, a minority is left-handed and an indeterminate number of people are best described as ambidextrous. This is universally true for all human populations anywhere in the world. So what makes our right hands so preferable? And has this always been the case or did we adapt to be righties? According to archaeologist Natalie Uomini at the University of Liverpool, “there has never been any report of a human population in which left-handed individuals predominate.”

Lateralization of limb use usually starts in the brain. The left side of the brain typically has more control over the right side of the body and vice versa. Essentially, the brain’s left hemisphere helps control coordination in the right hand. Many scientists believe the division of neurological labor evolved out of efficiency—the two hemispheres of our brains can carry out different computations at the same time. This can also be observed in various fish, toads, and birds, which are more likely to attack prey spotted with their right eye.

It’s possible that as our hominin ancestors began walking on two legs, they were predisposed to begin using their hands differently. Cognitive scientist Stephanie Braccini and her team wanted to get to the bottom of this. They studied a group of chimpanzees and discovered that when apes stand on all fours, they display no hand preferences. When they were forced to assume an upright stance a lateral preference emerged—though it was just as likely to be left-handed as right-handed.

Stone tools that were made 1.5 million years ago by Homo habilis and Homo erectus do show evidence of species-wide right-handedness. By the time Homo heidelbergensis emerged around 600,000 years ago, there was a clear right-handed preference in societies—as evidenced in the wear of their teeth, which suggested food was brought to the mouth with the right hand.

Some argue language could be the source of this shift. Most people do the bulk of their linguistic processing in their brand’s left hemisphere. It’s possible, then, that as the left hemisphere evolved for language, the preference for the right hand was intensified as a side effect. This hypothesis is known as Homo loquens: the idea that lateralization was driven by the bipedal stance, while the preference rightward was driven by the evolution of language.

Proving this hypothesis is extremely difficult since we do not have the ability to run neurological tests on our ancestors. There is also some speculation that handedness can be influenced and changed by social and cultural mechanisms. More restrictive societies show less left-handedness in their populations than other, more permissive societies.

The hand-brain association is not a simple correlation. Studies conducted in the 1970s revealed that most left-handers have the same left-hemispheric brain specialization for language typical of all humans.

Source: Scientific American, BBC

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