Research Into Left-Handedness And Its Effects
There has been a huge amount of research done into various aspects of left-handedness, often without much in the way of clear conclusions. We will be using this section to provide articles and links for you to see and to let you know of current research that is going on that you could possibly participate in.
If you are involved in research into left-handedness or its effects, please let us know and we will include details in this section.
We have a lot more information to go in this section, so check it again next time you visit us.
Evolution may be in the process of delivering a new age of genius and creativity, with left-handers leading the way. Professor Chris McManus of University College, London has been researching the subject and is about to publish a new book called Right Hand, Left Hand. He is convinced that the proportion of left-handers is rising and left-handed people as a group have historically produced an above-average quota of high achievers.
He says that left-handers' brains are structured differently in a way that widens their range of abilities and the genes that determine left-handedness also govern development of the language centres of the brain.
In Britain, around 13% of men and 11% of women are now left-handed, compared to just 3% of those born before 1910. There are a number of factors driving this increase:
- Left-handers were severely discriminated against during the 18th and 19th centuries and it was often “beaten out” of people
- In adulthood, left-handers were often shunned by society, resulting in fewer marrying and reproducing
- As discrimination was reduced in the 20th century, the number of natural left-handers who stayed left-handed increased
- The rising age of motherhood contributed as, statistically, older mothers are more likely to give birth to left-handed children
The professor says that the increase could produce a corresponding intellectual advance and a leap in the number of mathematical, sporting or artistic geniuses.
Unfortunately, it is not all good news for left-handers. They tend to be over-represented at both ends of the intellectual scale and as well as geniuses the group also produces a disproportionately high number of those with learning handicaps. There have been suggestions of links between left-handedness and dyslexia, stuttering and child autism among others.
Left-Handers Club comment…
We have had a lot of anecdotal evidence of an increasing proportion of left-handers among young children and our correspondence with members supports the view that left-handers are over-represented at both the top and bottom of the learning and achievement scale.
Now that left-handedness is not actively discouraged and young left-handers can obtain basic tools like pens and scissors to allow them to learn and express themselves in their own direction, most stay as left-handers and do not have their naturally creative advantages interfered with.
We have known Professor McManus and his work for the past 10 years or so and we will give further comment on his current project when the results are published in full. We also hope that he will give us some further background and personal comments that we can pass on to our members.
The Left-Handers Club is planning a major series of surveys this year which will aim to discover which activities and occupations groups left-handers are over- and under-represented in and the factors that affect this. We will be producing further information on this and asking for assistance very soon.
Source: New Scientist, 22 October 2001, James Randerson
Having a close left-handed relative makes right-handers better at remembering events than those from exclusively right-handed families, new research suggests. There is a downside, however, as members of these ambidextrous families may be relatively impaired in their ability to recall facts.
According to the study, having a left-handed sibling or parent means the organisation of your brain is intermediate between a pure ‘lefty' and a pure ‘righty'.
Specifically, Stephen Christman and Ruth Propper at the University of Toledo, Ohio claim that people with ‘lefties' in the family have a larger corpus callosum – the connection between the brain hemispheres. This makes you better at certain memory tasks, but worse at others, they believe.
Two types of memories are involved. Episodic memories are those with a context that is separate from the information itself – for example, where you parked your car or where you left your keys. Semantic memories on the other hand are things ‘you just know', such as the dates of the First World War or the recipe for apple pie.
Filling the gaps
The researchers showed 180 right-handed subjects lists of words. Some of this group was asked to recall as many of the words as possible once the list had been taken away. This tests episodic memory because the subjects have to remember the words they were taught.
Others from the group were given fragments of words with a letter missing and asked to fill in the gaps. This semantic test simply relies on knowing how the correct word should be spelt. Subjects with close left-handed relatives did better at the first ‘remember' task, but worse at the second ‘know' task.
“The key difference is not whether you are right handed, but whether you are strongly or weakly handed,” explains Christman.
Making the connection
A definitive explanation for the results is still some way off, says Christman. But he suspects that it might involve the roles that different brain hemispheres play in memory. He believes the information itself tends to be stored in the left hemisphere, while the place and time context resides in the right.
Both these components will be useful in episodic memories, so he suspects that people with a large corpus callosum linking their hemispheres – such as those from more ambidextrous families – will do better at these tasks. Semantic memory requires only one hemisphere, so it may be that those with fewer connections between the hemispheres have less interference and perform better.
Chris McManus, an expert in handedness at University College London, agrees that people with left-handed relatives have a brain that is “slightly more like that of a left-hander”.
But he is sceptical about Christman's explanation. The link between a weak-handedness and a large corpus callosum is “distinctly controversial”, he says.
Journal reference: Neuropsychology (vol 15 (4)
Leading British psychiatrist Prof. Tim Crow believes he can show that ambidextrous children are less intelligent than their peers – and his theory could even shed light on schizophrenia.
Unlike our closest genetic relative the chimp – who is truly ambidextrous – humans tend to heavily favour one hand and struggle to perform simple tasks with the less favoured. Prof. Crow, of the University Oxford, believes this difference could be crucial to the evolution of humankind around 137,000 years ago. The development of a division in function between the left and right sides of the brain – which result in our tendency to be right or left-handed – was a major factor in our leap from Homo erectus to Homo sapiens.
“Handedness is the key dimension of human cerebral function,” says crow. “People who are truly ambidextrous are slower to develop verbal and non-verbal skills. It's the predictor of both reading difficulties at the age of 16 and psychosis”.
For his study, Crow analysed data taken from 12,770 1 year old children taken in 1969 as part of the UK National Child Development Study. The children had been tested for hand preference, verbal, reading and mathematical ability. The test immediately resolved the age-old argument over whether right or left-handers are more intelligent : the answer is that there is absolutely no difference between them. What was startling was how badly ambidextrous people performed in the study – they did dramatically worse in all 3 tests. Youngsters who were extremely right or left-handed also tended to do poorly, but not as badly as the ambidextrous children.
“There seems to be an optimum level of handedness at which we perform best, although we are not sure what that is” said Crow. “Most of the variation in intelligence is to do with the degree of handedness in the child.”
Crow is aware these results may anger the parents of ambidextrous children, but he stresses that more research is needed to interpret the results fully. “The problem is that intelligence is a nebulous concept” he says. “These children may simply be late developers. Or they may be developing in a completely different way.”
Crow says that the gene responsible for encouraging specialist functions in one side of the brain, such as handedness, is what allows us to develop advanced skills, and without it the language centre of the brain would not have been able to develop. It is this development of language that differentiates us from the animals, and Crow's research continues into pinpointing exactly which gene or group of genes this is.
The consequences of this could be controversial, since they raise the possibility that we may one day be able to manipulate the very genetic material which makes us human. However, although this gene may set us apart from the apes there appears to be a cost. Crow believes that the same genetic changes that allowed the development of language by creating imbalance in the brain also created the potential for schizophrenia. “It is the price that Homo sapiens pay for language” he says.