Hand Dominance and Preference With Twins

Are your twins right-handed or left-handed? Or perhaps they are one of each? Or even ambidextrous? Twins have played an important role in the scientific research about handedness, although in many ways they muddle the mystery more than resolve it.

Handy Facts on Handedness and Twins

• Less than 10% of the population is left-handed.
• There are slightly more left-handed males than females.
• About 20% of all identical twin pairs have one right-handed twin and one left-handed twin.

Various customs and beliefs are associated with left-handedness in cultures around the world and throughout history. Unfortunately, in most cases, left-handedness is linked with sinister or dubious characteristics. For example, according to an indigenous Oneida Nation creation story, the world was created by a set of twin gods. The right-handed twin created beautiful landscapes, plants, and natural creatures. But the left-handed twin changed what the right-handed twin had made so they were no longer good. For example, he made pure springs into poisonous waters and turned edible plants into poison.

How Handedness Happens

Many people assume that hand preference is a genetic trait. However, that is not completely the case. A quick survey of identical twins with different handedness will confirm the discrepancy. Researchers have worked to identify a genetic link. One study found that even when both parents are left-handed, their offspring are more likely to be right-handed, although there's a greater chance of being left-handed compared to having parents who are right-handed.

There are many theories as to why people display a preference for one hand over the other. It is believed that a combination of genetic and environmental factors come into play. One theory projects that position in the womb determines handedness, which would make sense for twin pairs who are right and left-handed since they're likely to lie in opposing directions in the womb. Another theory suggests that left-handedness occurs due to stress or trauma during pregnancy or birth, nothing that a twin pregnancy is inherently stressful due to multiple fetuses.

On the Other Hand

While all of these theories are interesting, none fully satisfies the issue, because they don't hold true for all babies. Another theory also postulates that prenatal experience influences handedness, explaining that increased levels of testosterone exposure in the womb decrease the development of the left hemisphere of the brain. That would explain the higher incidences of left-handedness in males, but also among multiples since hormone levels are increased during pregnancy with multiples.

It Works for Me

That would seem to explain my twins' situation. One of my twin daughters is left handed, and one is right-handed.