Language
gene found
http://www.nature.com/nsu/011004/011004-16.html
The first linking of a gene to language could speed our understanding
of this most unique and most controversial of human abilities.
4 October 2001
JOHN WHITFIELD
Language
problems run in the 'KE' family. Members of several generations
speak "as if each sound is costing them their soul",
one researcher has said. They struggle to control their
lips and tongue, to form words, and to use and understand
grammar. "To the naive listener, their speech is almost
unintelligible," says geneticist Anthony Monaco, of
the University of Oxford in England.
Researchers
today unveil the single gene that, when it goes wrong, causes
this speech breakdown. The gene - the first to be definitively
linked to language - switches others on and off, and so
could lead the way through a genetic network of language
learning and use.
Finding
one gene is like finding one part of a car. It looks useful,
as though it's part of a larger mechanism. But we don't
know what it does, what other parts it interacts with, or
what the whole vehicle looks like. "It's an unbelievably
complex system, and we've got one tiny glimpse," says
Michael Tomasello, a psychologist at the Max Planck Institute
for Evolutionary Anthropology in Leipzig, Germany.
We shouldn't
have to wait long for more parts to turn up. Geneticists
are on the trail of genes that control brain development
and affect a range of mental disorders. The human genome
sequence lets them do much of the groundwork on a computer,
"saving what used to be months of work", says
Robert Plomin, a behavioural geneticist at London's Institute
of Psychiatry.
Forked
tongue
The
study of language divides researchers almost as starkly
as languages themselves divide us. They disagree about whether
language abilities are an innate feature of our biology
or a product of our social interactions. Their opinions
differ about whether the brain's language centres are specialized
for these tasks alone, or are a part of our general mental
machinery.
The
controversy centres on theories first put forward by Noam
Chomsky in 1959. That children learn to talk without instruction,
and that adults construct an infinite number of new sentences
from a finite number of words, convinced Chomsky that humans
possess an inbuilt 'universal grammar' - a set of rules
about the structure of language.
Forty
years on, these ideas remain controversial. "You have
to decide which side you're on - there's not much middle
ground," says Bruce Tomblin, who studies the genetics
of speech disorders at the University of Iowa in Iowa City.
Tomasello, for example, believes that it is our ability
to use abstract symbols that distinguishes humans from other
animals, and is more likely to be genetically encoded in
some way. Grammar, he says, "emerges historically -
it's a sociological product, not genetic".
You
don't need to believe in special language genes to believe,
like Chomsky, in specialized, uniquely human language structures
of the brain. "I don't think there are genes just for
language, rather that genes build brain structures in such
a way as to inform children what to expect," says Martin
Nowak, who studies the evolution of language at the Institute
for Advanced Study in Princeton. "It's impossible to
learn language if we don't have a brain structure defined
to expect it."
Family
code
Family
KE was first described in 1990. The way the disorder was
shared out between the generations made it clear that just
one gene was responsible, and the discovery was initially
trumpeted as a 'gene for grammar'. When the breadth of the
family's impairments became clear, there was a retreat from
this claim - "I've heard it called the cold fusion
of our field," says one psychologist.
The
controversy still smoulders over whether the KE's symptoms
have more to do with their inability to control their mouths,
or some general brain problem, than with language centres.
Supporters of a more purely linguistic interpretation of
the family's difficulties point to the fact that the family's
IQ, although below average, is within the normal range.
Monaco's
team had been hunting the KE gene for several years. By
1998, they had pinned it down to an area of chromosome 7.
Data from the Human Genome Project suggested that there
were about 70 genes in this area. "We were marching
down the chromosome," he says, using genetic markers
to progressively narrow down the area that might contain
the gene.
Two
years ago, their march became a run. 'Patient CS', an unrelated
boy with very similar difficulties to the KEs, turned up.
Comparing the two allowed the researchers to stop their
laborious rummage through chromosome 7 and zoom in on the
gene. "It probably saved us a year or two," says
Simon Fisher, another member of the Oxford team.
The
same gene, called FOXP2, is damaged in the new patient and
in the afflicted KEs. It belongs to a group that controls
the activity of other genes by making a protein that sticks
to DNA. The mutations in family KE and patient CS disrupt
the DNA-binding area of the protein.
FOXP2
is "an important piece of the genetic puzzle of language",
says psychologist Karin Stromswold of Rutgers University
in New Jersey. But most language impairments are nowhere
near as severe as those afflicting the KEs, and the patterns
of inheritance in most families with language disorders
are also more complex. The gene's "very messy"
effects necessitate further studies of families with more
limited impairments, cautions Stromswold.
Monaco's
team is currently scanning the genomes of such families."I
would be extremely surprised if the FOXP2 gene were a major
determinant of more specific language impairments,"
he says.
FOXP2
is not unique to humans - it is switched on in the lungs
and brain of mice. But subtle differences in its sequence
or workings may illuminate why humans talk and animals don't,
and how our ability evolved.
Ultimately,
"we need to understand how genes give rise to brain
structure, and how our brain structure gives rise to language",
says Nowak. This job is just beginning: a full grasp of
such processes is "50 to 100 years away", he says.
Shaking
the tree
The
network of language genes may be like a tree. Genes such
as FOXP2 could be at the trunk - where sawing through them
would knock out lots of aspects of language. Other genes
might fine-tune aspects such as grammar further down the
line; knocking these out would be analogous to lopping off
a branch.
Psychologist
Heather Van der Lely, of University College London, subscribes
to this school of thought. She studies children whose speech
and understanding of individual words are fine, but who,
like normal adults learning a foreign language, are unable
to master grammar. Such children muddle their tenses, saying
'yesterday I jump the fence', for example, and struggle
to phrase questions.
"You
have to explicitly teach them the rules of language,"
says Van der Lely. "They never have an intuitive knowledge
- they always have to stop and work it out." These
are the kind of 'pure' language deficits Stromswold wants
gene-hunted. They lead van der Lely to believe in specialized
grammar circuits in the brain, and genes to control their
development.
Unsurprisingly,
not everyone agrees. "It's hard for me to believe that
we have genes devoted to influencing the brain in very specific
ways that affect language and only language," says
Tomblin. He thinks speech emerges from "general-purpose
cognitive mechanisms, some of which may be more important
for language than others. It's a less tidy view of things,
but as I see the data, it looks more tenable."
Even
apparently pure language disorders may be caused by complex
interactions of many factors, warns Plomin. He believes
there may be lots of different ways - genetic errors or
environmental insults - to reach the same end language problem.
Sliding
scale
People
differ widely in their linguistic ability and behaviour
- the age at which they begin speaking, for example, and
the speed with which they master language. Plomin says that
language development is probably controlled by "many,
many genes, each with a small effect, working in many bits
of the brain". Rather than language being something
that you've got or you haven't, says Plomin, all these genes
conspire to place people somewhere on the scale of linguistic
ability.
Plomin
is involved in a study of 16,000 pairs of British twins.
It has found a strong heritable component to language disorders,
but individual genes are hard to pin down: "I'm optimistic,
but progress has been a lot slower than people thought it
would be," Plomin says.
The
genes and brains of unusually gifted linguists, people who
can speak many different languages fluently, for example,
might also reveal other genetic contributions to language
learning. This approach has been neglected, Stromswold says,
but a "surprising number" of professional linguists
are the offspring of other linguists. "Linguists who
marry linguists should trot on down to their local genetics
centre," she adds.
It would
be particularly interesting if their brains didn't work
so well in other areas. "I'd look for linguists who
can't balance a cheque-book," Stromswold says.