Knowledge is passed down directly from generation to generation in the animal kingdom as parents teach their children the things they will need to survive. But a new study has found that, even when the chain is broken, nature sometimes finds a way.

Zebra finches, which normally learn their complex courtship songs from their fathers, spontaneously developed the same songs all on their own after only a few generations.

"We found that in this case, the culture was pretty much encoded in the genome," said Partha Mitra of Cold Spring Harbor Laboratory in New York, co-author of a study in Nature on Sunday.

Birds transmit their songs through social interactions, as humans do for languages, dances, cuisine and other cultural elements. Though birds and humans have clearly followed different evolutionary paths, birdsong culture can still inform theories of human culture.

Normally, male finches learn their complex courtship songs (MP3) from their uncles and fathers. But if there are no vocal role models around, the song will deviate from the traditional song and be harsh to female finch ears (MP3). Each bird, then, must learn from his father or uncles, as they learned from their fathers, and so on — but this can only take us so far down the lineage.

“It's the classic 'chicken and the egg' puzzle,” Mitra said. “Learning may explain how the son copies its father's song, but it doesn't explain the origin of the father's song.”

Mitra's team wanted to find out what would happen if an isolated bird raised his own colony. As expected, birds raised in soundproof boxes grew up to sing cacophonous songs.

But then scientists let the isolated birds give voice lessons to a new round of hatchlings. They found that the young males imitated the songs — but they tweaked them slightly, bringing the structure closer to that of songs sung in the wild. When these birds grew up and became tutors, their pupils' song continue to conform, with tweaks.

After three to four generations, the teachers were producing strapping young finches that belted out normal-sounding songs.

You can listen to the progression below, but keep in mind that the elements that are important to female finches – duration of beats, rise and fall of pitch – can be difficult for the untrained human ear to pick up on. (QuickTime works best for these)

birds raised in isolation (MP3)

first generation (MP3)

second generation (MP3)

third generation (MP3)

fourth generation (MP3)

wild birds (MP3, MP3)

“It all happened so fast, and there was so little difference between the colony and in the one-to-one tutoring environment,” said lead author Olga Fehér of City College of New York. “So the process is pretty much hardwired. And the interesting thing was also that they could only get so close in a single generation, so the three to four generations were necessary for the phenotype to emerge."

"Song culture can emerge 'from the egg,' as it were, if one allows for multiple generations to elapse," Mitra said. "In a similar way, we may 'grow' our languages."

Though there are approximately 6,000 different languages in the world, they all share certain structural and syntactic elements. Even when a language arises spontaneously, as it did in the 1970s among deaf school children in Nicaragua, it adheres to these stereotypical human language features.

The study's findings might have implications beyond language to other culturally-transmitted systems, said evolutionary biologist and cognitive scientist Tecumseh Fitch, at the University of St. Andrews.

"We can think about both birdsong and human culture — especially language but including other aspects of human culture, like music, cuisine, dance styles, rituals, technological achievements, clothing styles, pottery decoration and a host of others — in similar terms," he said. These culturally-transmitted systems must all pass through the filter of biology.

"Look at all the different human cultures," said Mitra. "They're different, but they're all within certain constraints, so those differences aren't genetic. But now compare with the chimp culture — there are key differences. The possibilities between those cultures are constrained by biology."

Mitra admits that the analogies between bird culture and human culture are tenuous. “But there are resemblances. Culture is just learned behaviors. The motivating scenario is, if you isolate human babies from culture, put them on an island and come back after a few generations, what would their culture be like? What sort of language would they have? What sort of politics would evolve?"

That experiment probably won't take place in the near future. In the meantime, Fitch says we can learn valuable lessons about human culture from songbirds, both at theoretical and mechanistic levels.

"Social learning is shared between the two, and songbirds are a well-understood and experimentally tractable system," he said. "These biologically-grounded studies will lead us beyond the tired 'nature versus nurture' or 'biology versus culture' dichotomies which dominate the social sciences today."

See Also:

Citation: Olga Fehér*, Haibin Wang, Sigal Saar, Partha P. Mitra & Ofer Tchernichovski. "De novo establishment of wild-type song culture in the zebra finch." Nature, published online ahead of print May 3, 2009.*

Image: Flickr/NeilsPhotography