What are the genetic basis of language? Mutations of the gene FOXP2 cause developmental verbal dyspraxia (DVD), a speech and language disorder that compromises the fluent production of words and the correct use and comprehension of grammar. But is FOXP2 role in audio communication a human innovation?
It seems not. Sebastian Haesler and collegues in Berlin have tried to suppress FOXP2 function in live zebra finchs , a cute Australian bird that is often used for study on learning. Male zebra finchs, in fact, learn their song from their parents.
The image above, from the Haesler paper, shows that the birds lacking FOXP2 function are much less accurate in imitating their parent's song. While the controls' spectrograms nearly perfectly match those of their tutors, FOXP2 defective birds struggle to imitate them but with evidently poor results. Most strikingly, the defects are similar to those of children born without a properly functional FOXP2 gene.
What does it mean? The neuromolecular basis of language are not a human innovation: they are shared by birds and humans. The same gene controls speech/song learning and production in both species nervous system. This means, amazingly, that the basis for speech-like audio communication were laid before the split between Synapsida (mammalians and extinct "mammalian-like" reptiles) and Sauropsida (other reptiles, including birds). It must have been some reptile-like amphibian in the moist forests of Carboniferous, more than 330 millions of years ago, to first emit the progenitor of both birdsongs and human songs.
Full open access paper on PLoS Biology, where you can also listen the normal and FOXP2-impaired zebra finch songs!