Tuesday, December 20, 2011

365 days of Twinipedia - Day 2

Day Two of  Twinipedia:

Fact #2:
This is an interesting fact...Did you know that up to 22% of twins are left-handed. In the general populace, only 10% are left-handed.

Here are some ideas explaining maybe why twins may be more likely to be left handed then the rest of the populace.  This information was found in the article titled Right Handed or Left Handed -Twins and Hand Preference; Twins Can Be Right Handed or Left Handed or Perhaps One of Each By Pamela Prindle Fierro, at About.com Guide 


...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."...


  1. I honestly chalk our twins up to my age. When I conceived I was 34, thus I have assumed that I 'dropped' two eggs. My boys are NOTHING ALIKE. I don't even think they look remotely alike at all! When people ask (as you know they do) we say yes, my great grandfather had twins...but I do not tell them that we also had sex at least once a day in my ovulating window :)

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