Whether a person favours their right hand or their left, and what this reveals about brain function, has been studied for at least 150 years. However, researchers still donít understand why around 10 per cent of the population turn out to be left-handed.

In the past, children who were naturally lefthanded
were encouraged or forced to use their
right hand, mainly because of prejudice against
the awkwardness of left-handed writing and the
prevalence of ‘right-handed’ utensils. These days,
left-handedness is more accepted.
If your child is naturally left-handed, don’t try to force
them into using their right hand. While we know very
little about what influences hand preference, we
do know that handedness reflects the wiring of the
individual brain.

CAUSES OF LEFT-HANDEDNESS
Just why one in 10 people favour their left hand
is a mystery. A straightforward genetic link hasn’t
been proven, and it is possible for two right-handed
parents to have a left-handed child. Theories
include:
Genes
Perhaps genetic factors predispose a child to
favour the right hand. A single gene might be
passed from parents to children to influence
which hand a child favours. If a particular
version of this gene is inherited, the child may
be more likely to be left-handed, depending
on reinforcement and other environmental
influences. However, more recent research
suggests it is more likely that lots of different
genes ‘add up’ to produce a left-handed
person.
Sex
Slightly more boys than girls are left-handed.
This suggests to some researchers that the male
hormone testosterone has an influence on right
and left-handedness.
Foetal development
Some researchers believe that handedness has
more of an environmental influence than genetic.
They propose that environmental factors in the
womb (including exposure to hormones) may
influence whether we favour the right or left hand
later in life.
Modelling
Children learn to choose their right or left hand by
copying parents and other significant caregivers.
However, this doesn’t explain why right-handed
parents sometimes have left-handed children,
and vice versa.
Brain damage
A small percentage of researchers theorise that
all human beings are meant to be right-handed,
but some type of brain damage early in life
causes left-handedness. For left-handers and
parents of lefthanders, it is important to note
there is no hard evidence to support this rather
controversial theory.
Adjustment
Some people who are naturally right-handed
become left-handed because of the need to
adjust to injury.

THE DEVELOPMENT OF PREFERRED HANDEDNESS
Very young children often use both hands equally.
Hand preference in the early years seems to rely
on which hand is closer to the desired object; for
example, a toddler may reach for a toy on their left
side with their left hand because of convenience,
regardless of future hand preference.
Most children have a preference for using one
hand or the other by the age of about 18 months,
and are definitely right or left-handed by about
the age of three. However, a recent UK study
of unborn babies found that handedness might
develop in utero. About nine out of 10 unborn
babies preferred to suck their right (rather than
their left) thumb, and this hand preference was
borne out later in life.

RESEARCHERS STILL LOOKING FOR ANSWERS
The brain has two hemispheres, the left and the
right. Researchers into the brain once believed
that handedness revealed which brain hemisphere
was dominant. However, if this were true, it would
indicate that other functions controlled by the brain
should be influenced by this ‘dominance’. This
doesn’t appear to be the case; for example, the
speech centres tend to be located on the left side of
the brain, regardless of hand preference.
Another difficulty for researchers is that handedness
isn’t always cut and dried. While some people use
one hand exclusively for all tasks, others tend to
swap depending on the activity; for example, some
people write with their left hand but open jars with
their right.
It was once believed that a right-handed person
has general dominance on the right side of their
body, which means their favoured foot, eye and
ear are also on their right side. We now know this
isn’t the case. Many people may be right-handed
but, for example, always take the first step with
their left foot. The more we find out about right and
left-handedness and their links to brain function, the
more we realise we don’t know.

CROSS LATERALITY EXPLAINED
Cross laterality is an ambidextrous mixture (for
example, being left handed but dominant in the
right eye and foot). This may cause coordination
difficulties. However, some sports (such as
gymnastics) benefit from the distribution of brain
dominance. Research into cross laterality is
ongoing.

PROBLEMS FOR LEFT-HANDED PEOPLE
Since 90 per cent of the population is right-handed,
left-handed people do experience some practical
problems, including:
- Western writing runs from left to right. A lefthanded
person has to ‘crab’ their hand in order to
write without smudging the ink.
- Left-handed children learning to write often
write back to front (‘mirror’ writing). This is
a natural inclination, not a sign of dyslexia,
and will resolve given time, practice and
encouragement.
- Implements such as scissors are designed for
use with the right hand.
- Tools such as circular saws can be dangerous if
operated with the left rather than the right hand.
- Some research has suggested that learning
difficulties, epilepsy and autism are more
common in left-handed people. However, other
researchers have been unable to confirm these
findings and current knowledge suggests that
handedness is not associated with learning
disabilities.

ADVANTAGES FOR LEFT-HANDED PEOPLE
Being left-handed also has its perks, including:
- Left-handed people are at an advantage in a wide
range of sports, from fencing to boxing
- The sporting advantage also includes taking the
right-handed opponent by surprise, because righthanded
athletes aren’t used to playing against
left-handed opponents.

WHERE TO GET HELP
- School teacher and principal (in the case of a
child’s writing difficulties)
- Your doctor

THINGS TO REMEMBER
- Researchers still don’t understand why around
10 per cent of the population turn out to be lefthanded.
- Most children have a preference for using one
hand or the other by the age of about 18 months,
and are definitely right or left-handed by about the
age of three.
- If your child is naturally left-handed, don’t try to
force them into using their right hand.

Article provided by the Better Health Channel.
Visit www.betterhealth.vic.gov.au for further
information and fact sheets.