Flattening disease curves and avoiding disease outbreak spikes are current hot topics. Facebook posts associating left-handedness with a variety of clinical conditions are also experiencing a frequency spike. To be sure, there is a long history of connecting left-handedness to disorders and diseases. This trend started in the 19th and continued into the 20th century. The latest manifestation occurred in the early 1990’s when left-handers were labelled alinormal. Left-handers appear as normal as right-handers but internally their compromised physiology puts them at higher risk for contracting disease. Hence, left-handers are alinormal rather than normal. This theory was subsequently discredited by many research papers but it seems resistant to complete extinction.
I cannot be more emphatic. The era of associating left-handedness with disease is coming to a close, if not at a complete end. Left-handedness is not a pre-existing condition that increases an individual’s disease susceptibility. Several recent studies using samples of thousands of participants report no difference in rates of disease when left- and right-handers are compared.
The connection between left-handedness and schizophrenia is often mentioned. Schizophrenia is a developmental brain disorder characterized by hallucinations and delusions. The movie, A Beautiful Mind, starring Russell Crowe as the mathematician, John Nash, portrays the symptoms of this disease in a dramatic way. Nash not only experienced the ongoing presence of an hallucinatory roommate, he also had the delusion of being involved in a secret government mission. Research evidence indicates that schizophrenics have higher rates of mixed-handedness, not left-handedness, when compared to non-schizophrenics. Many people are mixed-handed using the right hand for some activities and the left hand for others. Schizophrenics can show an unusual form of mixed-handedness where they switch hand use within an activity. For example, a person may write with the right hand on one occasion and switch to writing with the left hand at another time. Researchers call this atypical form of mixed-handedness, ambiguous handedness, because preferred hand use is ill-defined. Ambiguous handedness signifies that lateralization is not firmly established among a percentage of schizophrenics.
The relationship between schizophrenia and mixed-handedness has been reported in a number of studies. Unfortunately, these scientific findings are often misinterpreted to mean that handedness type precedes the disease and is its cause. The truth is the reverse. The anomalies of brain development found in schizophrenia also cause the atypical lateralization patterns in some individuals with schizophrenia. Mixed-handedness is a symptom of schizophrenia not its cause.
Occasionally, a left-hander posts a query on Facebook that reads What if left-handers were considered normal? Good news! Scientific evidence supports left-hander normalcy. Their handwriting position may be in the minority but in all other respects left-handers are as healthy and normal as right-handers. One must keep in mind the following scientific principle when assessing differences between handedness types. The within-group differences are often greater than the between-group differences. In other words, an individual left-hander is more likely to differ from another left-hander in a variety of ways than to differ from a right-hander.