LINK: http://www.rense.com/general20/dh.htm
Left-handers
have different brains
People who grow up left-handed have a different, more
flexible brain structure than those born to take life by
the right hand, say researchers at the University of
California, Los Angeles, who used twins to study heredity.
The reason is that right-handers have genes that force
their brains into a slightly more one- sided structure,
according to research published yesterday in the
Proceedings of the National Academy of Sciences.
Left-handers appear to be missing those genes.
"There really is a difference in brains that results in a
more symmetric brain in left-handers, where the two sides
are more equal," said UCLA neurogeneticist Daniel
Geschwind, who led the research team. "There is more
flexibility, and that is under genetic control."
In the effort to understand how the brain shapes the mind,
researchers have been striving to document the way genes
and environment affect intelligence and mental abilities.
The human insistence on preferring one hand over the other
poses a particularly nagging question that touches on both
anatomy and behavior.
"There is clearly something fundamental here we need to
comprehend if we are to understand what makes us uniquely
human," Geschwind said.
Of all the primates, only human beings display such a
strong predisposition to right-handedness. Right-handers
make up about 90 percent of the population. The left and
right halves of the brain are different in both their
anatomy and their functions, related in part to hand
preference.
But until now, no one could document the connection.
The UCLA study is the strongest evidence yet that heredity
shapes the brains of left-handed and right-handed people
differently, Dartmouth neuroscientist Michael Gazzaniga
said.
The UCLA researchers conducted brain scans on 72 pairs of
male identical twins between 75 and 85 years old.
Identical twins, who share the same genes, offer a unique
lens through which to study the relative effects of
heredity on human nature.
Right- and left-handedness is partially determined by
genetics. If a person inherits the gene for
right-handedness, that person will be right-handed. People
who do not have that gene, however, can be either left- or
right-handed. There is no specific gene for
left-handedness.
Right-handers typically have a larger left brain
hemisphere, where their language abilities are
concentrated.
Conversely, left-handers have more balanced brains, with
both sides relatively symmetrical. The language abilities
of left-handers more often are concentrated on the right
side.
If identical twins carry the gene for hand preference, both
must be right-handed. If they lack the gene, one twin can
develop right-handed while the other develops left- handed.
The researchers found that the brains of identical
right-handed twins were very similar in size and structure.
But when a left-hander was part of the twin set, the brains
were different. The conclusion, researchers said, is that
the absence of the gene for hand preference allows the
brain to develop differently as the individual grows up.
A similar pattern did not appear in 67 sets of fraternal
twins used as a control group.