Humans and finches may be birds of a feather when it comes to
learning how to speak and sing.
According to UCLA researchers, similarities between how humans
learn to speak and songbirds learn to sing may be rooted in shared
genes.
The researchers reported in the March 31 issue of The Journal of
Neuroscience that the zebra finch shares the genes FoxP1 and FoxP2
with humans. These genes play similar roles in the vocal learning
of humans and of zebra finches.
“Surprisingly, the expression (of FoxP1 and FoxP2) was
very parallel, suggesting they’re doing the same function in
both species, or perhaps an overlapping function,” said Dan
Geschwind, director of the neurogenetics program and associate
professor of neurology at the David Geffen School of Medicine.
It is hypothesized that FoxP2 is involved in vocal learning
““ how songbirds learn songs from their environments or
tutors, Geschwind said.
In humans, FoxP2 seems to play a vital role in the development
of the brain. Rare mutations of the FoxP2 gene have been found in a
few individuals in an English family, who have trouble
understanding and producing language.
Those affected by the mutation have structural abnormalities in
the brain.
Humans and songbirds share the natural ability to creatively
vary the sounds they make, said Stephanie A. White, assistant
professor of physiological sciences and co-author of the study.
Though many organisms, such as fruit flies, express FoxP2, they
do not express the ability to modify vocalizations
independently.
“You can train other primates for years and years and get
them to make new sounds, and it’s a lot of work,” White
said. “We do it naturally.”
FoxP2 is expressed in different tissues besides the brain and,
in the past, has been studied for a suspected role in lung
development.
FoxP1 and FoxP2 are both part of a family of genes called
transcription factors, which regulate other genes.
“(FoxP2) is necessary but not sufficient (for human
speech),” White said, confirming that there are other factors
that have not yet been discovered.
“We’re just really beginning to learn what the
connections are between genes that encode language and the language
that people use,” said Susan Curtiss, professor of
linguistics, who was not involved with the study, but researches
neurolinguistics and language acquisition.
“We have a good idea that certain speech disorders have
some genetic component to them, for example, stuttering,”
Curtiss said.
In addition to stuttering, the cause of another speech disorder
called Specific Language Impairment is also thought to be rooted in
genetics.
SLI can occur without the other symptoms of mental retardation
or social impairment.
The mutation of the FoxP2 gene is of interest to scientists
because it is the first case where a mutation of a single gene
gives rise to a speech disorder, White said.
Many genes ““ some which have not yet been identified
““ are responsible for language acquisition and use.
“Language … is a complex trait,” White said.
In addition to spoken language, disorders can affect written
language as well.
Developmental dyslexia and other written language disorders also
seem to have some genetic components, Curtiss said.
Written language disorders and speech disorders are often
closely associated with each other.
“Many children who have SLI end up getting labeled as
developmentally dyslexic,” Curtiss said. “But it is not
the case that every developmental dyslexic has SLI.”
Although genetics contribute to the likelihood of these
disorders, many other environmental factors could cause them as
well.
Further research into the similarities between songbirds and
humans at the level of genes may reveal evolutionary
relationships.
“We have a correlation so far that gives us the green
light to test whether parallel mechanisms have evolved in both
humans and songbirds that enable vocal learning,” White
said.