This is a song sung by a brown thrasher. But that’s just one of the thousand
or more that it knows, and it’s not the only avian virtuoso. A wood thrush can sing
two pitches at once. A mockingbird can match the sounds
around it, including car alarms. And the Australian superb lyrebird has an incredible, elaborate song
and dance ritual. These are just a few of
the 4,000 species of songbirds. Most birds produce short, simple calls, but songbirds also have
a repertoire of complex vocal patterns that help them attract mates, defend territory, and strengthen their social bonds. Each songbird species
has its own distinct song patterns, some with characteristic
regional dialects. Experienced listeners can even distinguish
individual birds by their unique songs. So how do birds learn these songs
in the first place? How do they know to mimic the songs
of their own species? Are they born knowing how to sing? A lot of what scientists know about bird
song comes from studying zebra finches. A baby male zebra finch typically learns
to sing from its father or other males, starting while it’s still
a fledgling in the nest. First comes a sensory learning phase, when the baby finch hears the songs
sung around it and commits them to memory. The bird starts to vocalize
during the motor learning phase, practicing until it can
match the song it memorized. As the bird learns, hearing
the tutor’s song over and over again is helpful—
up to a point. If he hears it too many times, the
imitation degrades— and the source matters. If the song is played
through a loudspeaker, he can’t pick it up as easily. But hide the same loudspeaker inside
a toy painted to look like a zebra finch, and his learning improves. What if the baby never hears another
zebra finch’s song? Interestingly enough, it’ll sing anyway. Isolated finches still produce
what are called innate or isolate songs. A specific tune might be taught, but the instinct to sing seems
to be hardwired into a songbird’s brain. Innate songs sound different from
the “cultured” songs learned from other finches—at first. If isolated zebra finches
start a new colony, the young birds pick up
the isolate song from their parents. But the song changes
from generation to generation. And after a few iterations, the melody actually starts to resemble the cultured songs sung
by zebra finches in the wild. Something about the learning process
must be hardwired, too, drawing the birds towards the
same song patterns again and again. This means that basic information
about the zebra finch song must be stored somewhere
in its genome, imprinted there by millions
of years of evolution. At first, this might seem odd, as we usually think of genetic code as a
source of biochemical or physical traits, not something like a behavior or action. But the two aren’t
fundamentally different; we can connect genomes to
behavior through brain circuitry. The connection is noisy and quite complex. It doesn’t simply map single genes
to single behaviors, but it exists. Genomes contain codes for proteins
that guide brain development, such as molecules that guide the pathways
of developing axons, shaping distinct circuits. Birds’ brains
have so-called “song circuits” that are active when the birds sing. These circuits also respond to the song
of a bird’s own species more strongly than
to other species’ songs. So the theory is that a bird’s genes
guide development of brain circuits that relate to singing
and the ability to learn songs. Then, exposure to songs
shapes those neural circuits to produce the songs
that are typical to that species. Genetically encoded or innate behaviors
aren’t unique to songbirds. They’re widespread in the animal kingdom. Spectacular examples include the long-distance migrations
of monarch butterflies and salmon. So what does this mean for humans? Are we also born with innate
information written into our genomes that helps shape our neural circuits, and ultimately results
in something we know? Could there be some knowledge that is unique
and intrinsic to humans as a species?
