Throughout a regular day, we complete various activities such as writing, picking up a glass of water to drink, or passing a frisbee with a friend at the park. Majority of the people in the world would use their right hands to carry out these tasks, whereas around 10% would use their left. Their low numbers in the world has given left-handed people some advantages, such as in sports. For example, left-handed pitchers and batters in baseball might have an advantage playing teams that are used to dealing with right-handed players. The large skew in hand dominance has caused many scientists to wonder where and how the uniqueness of this trait appeared in the evolutionary journey of the human race.

The exact origins of this trait are currently unknown. Some scientists previously believed that there was a single gene that controlled which hand was dominant. From this gene you could get two dextral alleles, two chance alleles or one dextral and one chance allele. Two dextral alleles would generally cause a person to become right-handed. If a person had two chance alleles, then there would be a 50:50 chance of them being right or left-handed. If a person had one of each allele then they would most likely become right- handed. Later research suggested that multiple genes were collectively responsible for determining a person’s hand dominance. Scientists believed that these genes somehow affected how the brain developed and thus determined which side of a person’s body would be dominant.

Another theory is that hand dominance is not only affected by genetics but by environment as well. More people in western societies are known to be left-handed than in eastern ones because of cultural taboos. Many families force right-handedness upon their children because left-handedness is seen as dangerous or culturally unacceptable.

From an evolutionary standpoint, most of the world being right-handed signifies that this trait was selected for some reason. Scientists hypothesize that since the left side of the brain controls the right side of the body and is also where language is processed for humans, right-handedness could be a byproduct of a well- developed left hemisphere. A well-developed left hemisphere would mean a better ability to process language well, which is a favorable trait. This does not necessarily mean that people who are left-handed are at a disadvantage. In fact, studies show that left-handed people have a better connection between the right and left sides of their brain that process language. Though this doesn’t guarantee that people who are left-handed may automatically be fluent speakers, it does show that both left and right-handed people have their fair share of benefits.

Left-handedness in twins is also disputed, especially for identical twins. Because identical twins come from the same egg, their genes are thought to be identical yet some twins still display different hand preferences. This difference is speculated to be the effect of an increase in hormones during pregnancy or the theory that there is some sort of mirror-like quality to twins’ genes. Twins seem to have a slightly higher chance of being left-handed than the general public, though the reason for this is also unclear.

The complexity behind hand dominance has made it such a fascinating and unique trait that scientists and others interested will continue to explore it in the future. Learning about the strengths of both right and left- handedness in people can help us better understand the human body and brain.

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