London - Left-handed people have historically had a rough ride, labelled “cack-handed” and “sinister” - even forced at school to write with their right hand (as I was, leaving me with a somewhat clumsy ambidexterity).
Most people think of left-handedness as a genetic thing, and while there is a link, new evidence indicates left-handedness may often be the result of developmental glitches. This, in turn, may make lefties more susceptible to some mental disorders, as well as being accident-prone.
Being left-handed has even been linked to an increased likelihood of transsexualism, as well as of high-achieving brilliance.
The latest research on left-handedness comes from Yale University. Researchers claim their study shows it has a strong link with psychotic disorders such as schizophrenia.
While around one in ten people are left-handed, the study, published in this month’s edition of the journal SAGE Open, found that four in ten of those with schizophrenic illnesses are lefties.
That level of over-representation means that they appear to be four times more likely than right-handers to develop the illness. Jason Webb, an expert in child psychiatry who led the research, describes this difference as “striking”.
While the Yale researchers didn’t attempt to explain the link between schizophrenia and left-handedness, another new study suggests difficult conditions in the womb - such as toxins, stress or malnutrition - may increase the likelihood of children being born left-handed. That poor environment may also make them more vulnerable to developing schizophrenic disorders.
Researchers from Graylands Hospital in Perth, Australia, looked at the maternal health records of more than 1 000 high school students born in Belgrade in Europe. They found that the left-handed teens were far more likely to have been born to mothers who smoked while pregnant.
The left-handed students were also significantly more likely to have been born with a low apgar score. Apgar scores are used by medical staff to assess a baby’s well-being.
The score is compiled from a head-to-toe physical examination of the baby at birth, including the hips, heart, eyes and, for boys, the testes, to assess if the child has developed physically in a healthy way.
The Australian scientists believe their study shows that while left-handedness can be inherited genetically, many cases are acquired before birth through environmental problems suffered in the womb.
Inheriting left-handedness is not a clear-cut matter of a “leftie” gene, either. Even identical twins, who have 100 percent of the same genes, do not always share handedness.
A study of more than 50 000 identical twins by the Queensland Institute of Medical Research in Australia, in 2009, found that inherited genes account for just 25 percent of the chance of being left-handed.
The other 75 percent of the effect appears to be down to environmental factors, according to the study in the journal Neuropsychologia.
Problems in the womb may also explain why left-handedness appears to make children more accident-prone. This again may be a result of poor brain development due to conditions in the womb.
A study of more than 550 children in the journal Pediatrics found that the left-handed youngsters were about twice as likely as right-handers to have been injured badly and need hospital treatment.
Their parents were significantly more likely to describe those children as “more clumsy than average”, according to the study by Arkansas Children’s Hospital in America in 1993.
A Harvard University Medical School report this year suggests, however, that some of the difference in accidents may be due to the fact that lefties have to cope with a world tailored for right-handers.
“For example, left-handers might have more accidents when using power tools designed for right-handed workers,” the report says.
Perhaps the most surprising aspect of left-handedness comes from Richard Green, a professor of psychiatry at the Gender Identity Clinic, Imperial College London. His research has found that transsexual men and women are mainly left-handed.
This was based on a study of 400 male and 100 female transsexuals over four years. The study found that the majority were left-handed, which again goes against the trend for the rest of the population.
The study found an important clue, too, to suggest that the origins behind this association go back to the womb. For it also revealed that transsexuals’ fingerprints tend to have distinctively strong ridges.
Professor Green believes that hand preference and fingerprints are both formed in the first 15 weeks after conception.
He says their development in the womb is influenced by the sex hormone testosterone, and that this influence may also somehow underlie the gender dysphoria - feeling mismatched from the biological sex you are born with - which transsexuals experience.
However, other research, published in the Journal of the American Medical Association in 1992, suggests that left-handedness - and transsexualism - may be determined later in the baby’s development.
The study of male-to-female transsexuals, led by Diane Watson, a professor of psychiatry at the University of British Columbia, also found high levels of left-handedness.
But she said evidence shows that this can be related to stress suffered either by the mother when carrying the baby, or by the baby during a difficult birth, through prolonged labour, oxygen-starvation or breech delivery.
Thus, she believes that many cases of left-handedness can actually be determined around the time of birth.
Are lefties disproportionately brilliant? Albert Einstein, Leonardo da Vinci, Aristotle and Charles Darwin count among them.
So do Michelangelo and Rubens, Benjamin Britten, Paul McCartney and Jimi Hendrix, plus five of the seven most recent US presidents, including Barack Obama. David Cameron is also a leftie.
Chris McManus, professor of psychology and medical education at University College London, argues that left-handed people as a group have indeed historically produced an above-average quota of high achievers. He says that the different way many left-handers’ brains are structured widens their range of abilities.
It is thought they use both sides of the brain for tasks such as verbal processing, where right-handers use only the left side; or they use both hemispheres for a task where a right-hander would use only one.
Professor McManus adds that the genes which can determine left-handedness also govern development of the language centres of the brain. His studies have identified at least 40 genes that may contribute to making people into southpaws.
Professor McManus, author of the book Right Hand, Left Hand, says the proportion of left-handers is rising. Records show they represented only three percent of people born before 1910, compared with 10 percent now.
This may be due partly to the fact that widespread discrimination meant it was often “beaten out” of children.
As adults, left-handers were often shunned, resulting in fewer marrying and reproducing, he says.
As discrimination reduced in the 20th century, however, the number of natural left-handers who stayed that way increased.
Professor McManus adds that the rising age of motherhood has contributed as well, since, statistically, older mums are more likely to give birth to left-handed children, though the reasons why are not clear.
Professor McManus argues that the increase in left-handers could produce a corresponding intellectual advance among humankind and growth in numbers of mathematical and artistic geniuses, and other high achievers, such as those already mentioned.
Good news indeed. However, my vestigial left-handedness has simply rendered me the world’s clumsiest typist. It has also left me in a state of confusion over the words “left” and “right”. They both just seem the same to me! - Daily Mail