I frequently hear that left-handed people tend to be smarter or more creative. For example, a disproportionate number of musicians, presidents, and doctors are left-handed. Does being left-handed give you these traits or is it a correlation due to another factor? If true, why?
Here's a study from the 1975: http://informahealthcare.com/doi/abs/10.1080/03014467500000811
Verbal and performance scores in a standard intelligence test (WAIS) were considered in relation to patterns of hand preference (measured by questionnaire) in a large sample of the general population.
Left-handers and mixed-handers did not obtain lower scores than right-handers. Indeed, there was a tendency for subjects who reported that they could use either hand for at least one of the questionnaire tasks to obtain higher I.Q.s. Otherwise, there were no significant differences in I.Q. with the exception of a consistent sex difference, in that men achieved higher scores on both verbal and performance scales.
Most other studies have the same inconclusive results. What I suspect as the origin of this apparent myth is confirmation bias: Whenever a smart or otherwise famous person is left handed, this will get noticed, whereas the right handedness of famous people does not surprise anyone.
"Mensa often gets enquiries as to which we have more of - left handed members or right handed members? And whether which hand you use is linked to IQ.
So we recently began to collect statistics from new members. With the information collected so far 10.58% of new members are left handed and 89.42% are right handed. This appears to reflect estimates of the UK population as a whole.
Of course the data does not cover membership as a whole, and Mensa members do not represent everyone with a high IQ. However it seems that what hand you use does not necessarily correlate with IQ."
About the creative part and the left-right brain, that's something that has already been discussed at skeptics.
"I've heard that the left brain controls the logical aspects of the thought and right brain controls the creative. Is there any truth to such claims?"
In the case of Left Brain/Right Brain "function" has been interpreted as "thought." Thought and function are not the same thing.
Each hemisphere of the brain has specializations or function sets. Generally: Right hemisphere: Processing of visual and audiological stimuli, spatial manipulation. Left hemisphere: Linear reasoning and language functions.
How do we know?
... definite evidence for language lateralisation arose from studies in split brain patients. In these patients, the nerve fibres that connect the two hemispheres were severed in order to stop the spread of epileptic seizures from one hemisphere to the other ... studies of these split brain patients were carried out in the 1960s and 1970s by the Nobel Prize laureate Roger Sperry and his colleagues at the Californian Institute of Technology ... Sperry’s experiments yielded an amazing result: when split brain patients processed an object with their right hand, i.e. with their left hemisphere, they could easily name the object. In contrast, when an object was touched with the left hand, i.e. processed by the right hemisphere, they could not name it!
The whole "philosophy" of Left Brain/Right Brain was pulled from this information, not from further research. In other words, it's made up.
The notion of different hemispheric thinking styles is based on an erroneous premise: each brain hemisphere is specialised and therefore each must function independently with a different thinking style. This connection is a bridge too far: it uses scientific findings regarding functional asymmetries for the processing of stimuli to create conceptions about hemispheric differences on a different level, such as a cognitive thinking style. Furthermore, there is no direct scientific evidence supporting the idea that different thinking styles lie within each hemisphere. Indeed, deriving different hemispheric thinking styles from functional asymmetries is quite a bold venture, which oversimplifies and misinterprets scientific findings.
The above two quotes come from The left brain/ right brain myth.
Being a neurophysiologist, I suppose I ought to feel that progress has been made: in no other age could it have taken a mere twenty years to shift from a predominantly religious metaphor to a semi-scientific one. But the neurophysiologists and neuropsychologists who specialize in the human cerebral cortex are starting to view the left-righters with something of the wariness which the astronomers reserve for astrology." -William Calvin"
Officials in Mensa, the high IQ society believe as many as 20% of their members are left-handed."
This fact, has been circulating through the net. I don't think it's true.
I also will leave this comment:
"What we call “creativity” is so diverse that it can’t be localized in the brain very well. – Daniel Willingham, UVa"