Birds' 'sexy songs'

The zebra finch mixes up its songs

By Richard Black BBC science correspondent

Scientists are homing in on some of the key brain circuitry that enables certain birds to produce beautifully complex songs.

They have identified a key set of genes in the animals which seems essential for them to construct and modify their songs in much the same way as humans are able to mix up their words to make different sentences.

The discovery is being discussed here at the annual meeting of the American Association for the Advancement of Science.

The work is likely to help researchers better understand how humans speak.

'Smoking gun'

The songs of some birds - such as canaries, parrots and humming birds - are incredibly complex, and to some extent they are like human speech.

The order of sounds is important, like the syntax and grammar of human languages; and some bird species can change their songs, learning new sounds from the world around them.

Something then must be special in the brains of these birds. Erich Jarvis from Duke University thinks he has now finally discovered what it is.

"It's exciting for me because scientists have been looking for anything related to syntax complexity for the past 30 years in these birds. There have been some hints, but nothing that was really strong - you know, a 'smoking gun' as they call it nowadays."

What Dr Jarvis has found is that in the parts of the brains of these birds that are used for their songs, particular molecules are present in large quantities.

Question of sex

They are called glutamate receptors, and are responsible for building connections between nerve cells.

Dr Jarvis believes these large concentrations of glutamate receptors have evolved separately in at least seven types of bird. But why?

"We find that those species which have this ability to imitate human speech don't just imitate human speech - they imitate many things in the environment.

"And we think this has something to do with sexual attraction; the more stuff you can imitate, the more you can recombine in different syntax, the more likely you're going to attract the opposite sex."

Which begs the question: did humans too evolve complex speech to win sexual advantage?