Scientific American Mind-June/July 2007

( The similarity between avian song and human speech )
may extend all the way to the molecular level.
Birds that must
learn how to sing,
such as the zebra
fi nch, produce the
FOXP2 protein
(red) in area X
(blue) in their brain.
Birds that know
their songs at birth,
like the ring dove,
do not make
the protein.
duction of speech. We know now, however, that
this strict division is a little too cut-and-dried because
a number of other areas of the brain are
involved in both understanding and producing
speech. The human brain probably processes
spoken information in many areas of the brain
simultaneously.
The idea that the brain uses parallel processing
to understand and control speech is consistent
with another observation: in the KEs, parts
of the brain that are normally not involved in
speech are active. This activity could be a direct
consequence of the FOXP2 defect—a proper
amount of the transcription factor would have
made those areas behave normally—or it could
be a sign that the brain is attempting to compensate
for one of the other fl aws caused by the
mutation.
Differentiating between the direct and indirect
effects of FOXP2 is no simple matter. For
example, because the gene is active during the
embryonic stage, its dysfunction could disturb
brain development. The brain could be “wired”
incorrectly, or certain specialized nerve cells
could fail to form. On the opposite end of the
spectrum of possibility, the brain might develop
normally but run into problems with information
processing later on—for example, during the
phase when children learn to speak. The real effects
of the FOXP2 mutation probably lie somewhere
in between these two extremes.
Bird Babble
To probe further FOXP2’s effects on cognitive
development, researchers are turning to
animals for clues. The FOXP2 gene has been
identifi ed in primates, whales, birds and even
crocodiles; it is highly likely that all vertebrates
have it. The sequence of the gene in these animals
is almost identical to that in humans. For example,
only three of the 715 amino acids in the
mouse FOXP2 gene product differ from those in
the human version. The timing and location of
the gene’s expression in the brains of other species
are also very similar. So what is the FOXP2
gene doing in the brains of these animals, none
of which is capable of speech?
Although most animals have vocalizations
that seem to be innate, a few species—among
them songbirds, parrots, hummingbirds, some
marine mammals and bats—do learn vocal patterns
by imitating their parents. To some extent,
this process is similar to that of a human infant
making his or her fi rst efforts at learning speech.
At fi rst, baby sparrows can imitate only minute
elements of their future song, for instance. This
type of vocalization is referred to as subsong, and
it is similar to infant babbling. When the young
animal hears an example of what is correct, it
adapts its vocal output.
Through intensive practice, young songbirds
increasingly come to sound like their role models,
mastering the repertoire by the onset of sexual
maturity. As is the case with humans, songbirds
are dependent on what they hear to develop normal
vocalization. If songbirds are subjected to
loud noises, if they become deaf or if the feedback
from their “teacher” is interrupted, they
never learn to sing properly.
The similarities between learned avian song
Zebra Finch Ring Dove
70 SCIENTIFIC AMERICAN MIND June/July 2007
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