credit: RBerteig
Why are people-left handed?
There are several prominent theories on how people end up left-handed.
Some data:
- 1 in 10 people world-wide is a lefty
- the exact percentage of lefties varies over time and around the world
- left-handed parents are more likely to have lefty kids 13% – 26% depending on gender and handedness of spouse
- men are more likely to be left-handed
- the more lefties you know the more likely you are to be murdered
Theory #1.) They are born that way.
People are left-handed because of in utero introduction of testosterone and the presence of the LRRTM1 gene that increases left right asymmetry in brain development. Many studies indicate that motor functions are generally controlled in the opposite side of the brain from the outside of the body. So, a greater development on the right-hemisphere of the brain is supposed to result in a dominant left hand.
Theory #2.) It is taught
When babies are born they are not lateralized for handedness, so they may just start using their left hand and have enough success that they just stick with it. But, supposedly, many of these people will suffer from poor handwriting and fine motor skills because their brains are wired against their behavior. Some people think that this kind of cross-functioning may be a contributor to stuttering, as the brain flits from one hemisphere to the other while formating language.
Theory #3.) There is something wrong with them.
It is alleged that the occurrence of left-handedness in developmentally disabled and severely developmentally disabled are 2x – 3x worldwide rate. There is also allegedly a slightly higher percentage of lefties that have schizophrenia and other psychological disorders. This theory holds that damage to the left-hemisphere of the brain will result in the brain compensating by moving the processes to the right side.
Theory #4.) The devil.
Seriously, some people think the devil makes you left-handed.
Theory #5.) It is a matter of degrees.
The truth of the mater is that handedness is not actually binary. We usually indicate handedness by writing, but a large proportion of people perform a range of tasks with their non-dominant hand, and lateralization is independent across the body meaning the dominant hand, foot, eye and ear can all be different. Even though true ambidexterity is rare many people can sufficiently carry on daily activities with either hand.
So, being left-handed is like being gay; it is either nature, nurture, environmental, the devil, or a pointless distinction.
