Why are the majority of people right-handed and left-eyed?

Humans have a bias towards the left and right in the actions we take in our daily lives. For example, it is said that the majority of the population is right-handed, performing most manual operations with their right hand. On the other hand, it is said that there is also a 'dominant eye' when it comes to vision, and the majority of people tend to favor the left eye. Professor Gillian Forrester, a comparative cognition scholar at the University of Sussex, explains the reason why the majority of people are right-handed but left-eyed, citing the results of her own research.

Why most people are right handed but left eyed
https://theconversation.com/why-most-people-are-right-handed-but-left-eyed-227099

Human handedness: A meta-analysis.
https://psycnet.apa.org/doiLanding?doi=10.1037%2Fbul0000229

In many cultures, approximately 90% of the population is right-handed, and the left eye is known to recognize various visual information more quickly and accurately than the right eye.

The reason for this difference in behavior is that animals have left and right cognition, which Professor Forrester explains is because the left and right hemispheres of the brain control different things.

Until recently, it was thought that cognitive lateralization was unique to humans, but a study published in 2019 showed that not only humans but also other vertebrates have cognitive lateralization.

For example, young birds use their dominant eye to distinguish between grains and pebbles, and young birds that use their dominant eye to observe their surroundings are less likely to be eaten by predators than those with asymmetric vision.

According to a study published in 2004, the left and right hemispheres of the brain evolved during evolution because cognitive lateralization allows the brain to control different actions simultaneously. Also, if the right and left hemispheres controlled a single function equally, confusion and inconsistency could arise between the left and right hemispheres.

When cognitive bias occurs between the left and right, the probability should ideally be 50% each, but in reality, more people are right-handed and more people are left-eyed.

Handedness generates asymmetric flow during embryo development A study has shown that the gene that expresses the structural protein of the brain is related to this. According to this study, the proportion of left-handed people with mutations in this structural protein expression gene was higher than that of right-handed people.

Right-handedness or left-handedness may be determined at the embryonic stage before the fetus becomes a fetus - GIGAZINE

And Prof Forrester argues that aligning one's left and right bias with other animals in the group may confer social advantages. For example, animals that stay in sync with the pack during cooperative behaviour are less likely to be caught by predators. Conversely, the few animals that stray from the group are more likely to be targeted by predators.

Professor Forrester and his colleagues, working with researchers from the University of Sussex, University of Oxford, University of Westminster and other institutions, investigated handedness and eye dominance and their effects on 1,600 subjects of all ages and ethnicities. Participants were assessed for hand dominance using a color-matching board task and for eye dominance using facial images expressing emotions, and their behavior was checked for bias toward their handedness or eye dominance.

The research team divided the subjects into four groups based on their handedness and eye dominance: 'standard' (right-handed, left-eyed), 'right-biased' (left-handed, left-eyed), and 'reversed' (left-handed, right-eyed). The 'standard' group was the most common, accounting for 53% of the subjects, while the 'reversed' group was the least common, accounting for 12% of the total.

The study found that people with moderate handedness performed better on the task than those with extremely strong or weak handedness, suggesting that extreme bias may limit flexibility in performance.

'What's striking is that the group with the reversed profile had significantly lower social skill scores and were four times more likely to have been diagnosed with autism or ADHD than the other groups,' said Professor Forrester. However, the research team said it was not possible to determine whether this relationship was causal at the time of writing.

Professor Forrester added: 'This study shows once again that humans have an evolutionary history, much of which we share with other animals. If we want to truly understand our modern brains and behaviour, we need to study ourselves in the context of the wider animal kingdom.'

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