Are your twins right handed or left handed? Or perhaps, one of each? Twins have played an important role in scientific research of the handedness issue, although in many ways they muddle the mystery more than resolve it.
- Less than 10% of the population is left handed.
- There are about 50% more left handed males than females.
- 20% of all identical twin pairs have one right handed twin and one left handed.
Strange 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, an ancient Iroquois legend describes the creation of the world by a set of twins. The right handed twin created landscapes, plants and natural creatures. The left handed twin created snakes, thorns and storms!
How Handedness Happens
Many people assume that hand preference is a genetic trait. However, that is not the case. A quick survey of identical twins will confirm the discrepancy. Researches have studied to find a genetic link. A Canadian study found that even when both parents are left handed, their offspring are more likely to be right handed.
There are many theories as to why people display a preference for one hand over the other. One theory projects that position in the womb determines handedness. The ear that faces out of the womb receives the most input and stimulates development of the coordinating side of the brain. This would explain handedness in twins, since they're likely to lie in opposing directions in the womb.
On The Other Hand
While that's interesting, it doesn't fully satisfy the issue, because it doesn'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 decreases 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.
Finally, one specialist offers an explanation for the handedness discordance among identical twins. In the July/August 2003 edition of Twins Magazine, Dr. Geoffrey Machin explains the phenomenon of mirror image twins, who most often display opposite hand preferences. He explains it in reference to how monozygotic twins split after conception.
- "It is "likely that the split ... happen[s] so that the twins form side-by-side. This means that the twin-on-the-right has to hurry up and make a new left side, because the twin-on-the-left has taken it, and the other twin has to make a new right side. This is probably why one twin often has a dominant right brain and the other has a dominant left brain."
It Works For Me
That would seem to explain my twins' situation. One is left handed and one is right handed. What about your multiples? Take the "On The Other Hand" Poll.