What are the proportions of the two kinds of left-handed people?

Question

Many people are familiar with the idea of asymmetry in the brain. For example, some well-known areas for language are on the left side. It is possible for some left-handed people to have a brain that is completely flip-flopped, so for people like this the same language areas would be on the right side, for example. However, other left-handed people have a brain just like right-handed people, but just have the left hand dominant. What percentage of left-handed people fit either the flip-flopped or non-flip-flopped categories?

(Also, it occurs to me that there might be some right-handed people who have flip-flopped brains, but then right-hand dominant.)

Answer 1

Very interesting question. I haven't read anything about someone's brain being flip-flopped so that language areas would be on the other side of the brain. But that doesn't mean it's impossible. It simply means there isn't enough research on the subject.

Concerning left-handedness, I got the following statistics from wikipedia.org (http://en.wikipedia.org/wiki/Left-handed#Statistics_of_left-handedness)

"Approximately 10% of the population is left-handed. People who can use both hands equally well are ambidextrous. True ambidexterity is rare. Generally, there are about 10% more male left handers than female left handers (5.24% Male, 4.76% Female). Approximately one-third of identical twins are left-handed. [1] Statistically, the twin of a left-handed person has a 76% chance of being left-handed."

I found some very interesting articles on dominance, cross - dominance, and ambidexterity. I also found article on rare health conditions where organs are on the opposite side of the body. (Such as dextrocardia, where the heart is on the right side instead of the left). I know these aren't about being left-handed or right-handed. But it goes to show that body parts can be in the wrong places. I have provided links below.

Answer 2

Some research has been done on the possibility that left-handed people were actually one of a set of twins during pregnancy, but only one twin survived. The one twin, who did not survive was in fact right-handed, and the twin left to be born would carry the traits of being left-handed. Just something to think about.