This is an interesting fact...Did you know that up to 22% of 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
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."...