Cambridge IELTS 1, Test 2, Reading Passage 1 : Right and left-handedness in humans
Right and left-handedness in humans
Why do humans, virtually alone among all animal species, display a distinct left or
right-handedness? Not even our closest relatives among the apes possess such
decided lateral asymmetry, as psychologists call it. Yet about 90 per cent of every
human population that has ever lived appears to have been right-handed. Professor
Bryan Turner at Deakin University has studied the research literature on lefthandedness and found that handedness goes with sidedness. So nine out of ten
people are right-handed and eight are right-footed. He noted that this distinctive
asymmetry in the human population is itself systematic. “Humans think in categories:
black and white, up and down, left and right. It’s a system of signs that enables us to
categorise phenomena that are essentially ambiguous.’
Research has shown that there is a genetic or inherited element to handedness. But
while left-handedness tends to run in families, neither left nor right handers will
automatically produce off-spring with the same handedness; in fact about 6 percent of children with two right-handed parents will be left-handed. However, among
two left-handed parents, perhaps 40 per cent of the children will also be left-handed.
With one right and one left-handed parent, 15 to 20 per cent of the offspring will be
left- handed. Even among identical twins who have exactly the same genes, one in
six pairs will differ in their handedness.
What then makes people left-handed if it is not simply genetic? Other factors must
be at work and researchers have turned to the brain for clues. In the 1860s the French
surgeon and anthropologist, Dr Paul Broca, made the remarkable finding that
patients who had lost their powers of speech as a result of a stroke (a blood clot in
the brain) had paralysis of the right half of their body. He noted that since the left
hemisphere of the brain controls the right half of the body, and vice versa, the brain
damage must have been in the brain’s left hemisphere. Psychologists now believe
that among right-handed people, probably 95 per cent have their language centre in
the left hemisphere, while 5 per cent have right-side language. Left-handers,
however, do not show the reverse pattern but instead a majority also have their
language in the left hemisphere. Some 30 per cent have right hemisphere language.
Dr Brinkman, a brain researcher at the Australian National University in Canberra, has
suggested that evolution of speech went with right-handed preference. According to
Brinkman, as the brain evolved, one side became specialised for fine control of
movement (necessary for producing speech) and along with this evolution came right- hand preference. According to Brinkman, most left-handers have left
hemisphere dominance but also some capacity in the right hemisphere. She has
observed that if a left-handed person is brain-damaged in the left hemisphere, the
recovery of speech is quite often better and this is explained by the fact that lefthanders have a more bilateral speech function.
In her studies of macaque monkeys, Brinkman has noticed that primates (monkeys)
seem to learn a hand preference from their mother in the first year of life but this
could be one hand or the other. In humans, however, the specialisation in (unction of
the two hemispheres results in anatomical differences: areas that are involved with
the production of speech are usually larger on the left side than on the right. Since
monkeys have not acquired the art of speech, one would not expect to see such a
variation but Brinkman claims to have discovered a trend in monkeys towards the
asymmetry that is evident in the human brain.
Two American researchers, Geschwind and Galaburda, studied the brains of human
embryos and discovered that the left-right asymmetry exists before birth. But as the
brain develops, a number of things can affect it. Every brain is initially female in its
organisation and it only becomes a male brain when the male foetus begins to
secrete hormones. Geschwind and Galaburda knew that different parts of the brain
mature at different rates; the right hemisphere develops first, then the left. Moreover,
a girl’s brain develops somewhat faster than that of a boy. So, if something happens to the brain’s development during pregnancy, it is more likely to be affected in a male
and the hemisphere more likely to be involved is the left. The brain may become less
lateralised and this in turn could result in left-handedness and the development of
certain superior skills that have their origins in the left hemisphere such as logic,
rationality and abstraction. It should be no surprise then that among
mathematicians and architects, left-handers tend to be more common and there
are more left-handed males than females.
The results of this research may be some consolation to left-handers who have for
centuries lived in a world designed to suit right-handed people. However, what is
alarming, according to Mr. Charles Moore, a writer and journalist, is the way the word
“right” reinforces its own virtue. Subliminally he says, language tells people to think
that anything on the right can be trusted while anything on the left is dangerous or
even sinister. We speak of left-handed compliments and according to Moore, “it is no
coincidence that left-handed children, forced to use their right hand, often develop a
stammer as they are robbed of their freedom of speech”. However, as more research
is undertaken on the causes of left-handedness, attitudes towards left-handed
people are gradually changing for the better. Indeed when the champion tennis
player Ivan Lendl was asked what the single thing was that he would choose in order
to improve his game, he said he would like to become a left-hander.
