Hard-wired for a song
Posted: Tuesday, May 05, 2009 5:35 PM by Alan Boyle
McGovern Institute / MIT
Click for audio: Zebra finches may be hard-wired to sing a particular
kind of tune. Click on the image to hear CCNY researcher Olga Feher
explain how the tune changed over the course of generations.
|
A songbird's brain may be programmed to gravitate toward a particular kind of tune, even if it's been taught from infancy to sing to the beat of a different warbler, researchers say. They go on to suggest that a similar neural mechanism might be behind the way our brains handle language.
"I think we humans, and songbirds, are probably born with some innate predisposition to communicate in a particular way," Olga Feher, a biologist at The City College of New York, told me this week.
The findings from Feher and her colleagues appear in this week's issue of the journal Nature. The experiments suggest that phenomena rooted in a species' culture - for example, singing for birds, using language for people - may be rooted in a species' genome as well.
"People have theorized long and hard about how the evolutionary process applies to culture," another co-author of the study, Partha Mitra of Cold Spring Harbor Laboratory, said in a news release. "This experiment takes culture and puts it into a laboratory setting. We've tested some questions, asked by others over many years, in a mathematically and experimentally crisp manner and come up with a concrete answer."
The experimenters started out by raising zebra finches in isolation, in soundproof boxes. For decades, scientists have known that an isolated songbird's innate song is different from the song that is "learned" from its feathered tutors as it grows up. In fact, different genes come into play as a songbird's song matures. So does the classic zebra finch song emerge merely as a cultural norm among the songbird set, or is there some sort of hard-wired inevitability about the tune?
Chalk one up for hard-wired inevitability: It's true that an untutored male bird can come up with a song that sounds raspy, screechy, off-rhythm or overlong. But when it's time for that odd bird to tutor the next generation, his students start introducing variations that bring the song closer to the "cultured" norm. After just four generations, the isolated zebra finches are singing the species' standard song.
"There's no good reason for them to do that," Feher, who worked on the study for her doctoral thesis, told me. "We think it's most likely that they have genetically encoded some sort of biases that enable them to judge a song and make it more 'wildlike.'"
Ofer Tchernichovski, a CCNY biology professor and Feher's thesis adviser, said the same pattern emerged whether the isolated male birds were raised among their tutors one-on-one, or raised in a colony, or raised among female zebra finches, which do not sing.
"This is the first time that cumulative culture has been demonstrated in the lab," he told me. "Culture emerges from scratch under very controlled conditions."
The fact that the cultured song emerged so quickly meant that natural selection didn't play a role in fine-tuning the song. But the neural mechanism behind the fine tuning most likely is a product of evolution. "That would be really interesting to know - the functional part of this whole phenomenon," Feher said.
Perhaps the females are programmed to respond to a particular kind of song as a signal of reproductive fitness, and thus the males who possess the fine-tuning mechanism have a better chance of survival. "We just don't know," Feher said.
But there is some evidence that the human brain works the same way: The researchers noted that a similar phenomenon of language convergence has been observed among deaf children in Nicaragua. The individual children developed a rudimentary sign language in their homes, but that language quickly evolved into a sophisticated system when the children were put together in a school for the deaf.
"That's pretty much the only documented case of real, dramatic language convergence in humans," Feher said. Subsequent research, involving deaf Bedouins in Israel, have provided further insights into the processes that may (or sometimes may not) lead to language convergence.
Some may argue that language changes too rapidly to be influenced by our genes, but even those researchers acknowledge that genetics laid the groundwork for language to emerge in the first place.
The latest study suggests that our brains and birdbrains may not be as different as they seem. We all come up with some crazy, oddball ideas when we're left alone. The key step is to figure out how birds (and humans) decide which of those ideas should be preserved, and which should be thrown out.
"When the bird is deciding what it comes up with [in the song it learns], what are the parameters that the bird is deciding to attend to?" Tchernichovski said. "The bird does not seem to have any bias against imitating the wrong song. He just imitates and 'improves' it. ... Maybe the bird doesn't listen to himself like he listens to others."
In addition to Feher, Tchernichovski and Mitra, the team behind the Nature study includes Haibin Wang of Cold Spring Harbor Laboratory and Sigal Saar of The City College of New York. Click here to listen to an MP3 audio clip of multigenerational zebra-finch songs.
