I'm just going to quote from a press release that fell into my inbox. It's about a talk being given at the American Society for Human Genetics meeting by Raymond Clarke, who identified a gene disrupted in a family sharing a disorder of the vocal tract. They call the gene tospeak:
The most exciting breakthrough in their research came when Clarke’s group discovered that the tospeak gene was unique to primates. Most of the human genome contains genes that are older (i.e., conserved over generations) and can also be found in other mammals, including the mouse. However, the tospeak gene is a relatively young gene that is only found in primates. Further excitement came when the group discovered that the tospeak gene has a special control region, known as a promoter, which is only found in humans.
“The discovery that a unique and more powerful human gene/promoter was disrupted in this vocally impaired family is of particular interest to the field of evolutionary genetics, since humans are the only creatures that have developed the capacity to speak,” said Dr. Clarke.
Clarke provided the following example as a comparison to help explain this new discovery: “Unlike GDF6, a bone protein gene which has existed since the dawn of vertebrate evolution, the tospeak gene is only found in primates. The best indication of the role of tospeak in human vocal development is that it was the only gene disrupted in a large family with a severe vocal disorder, altered composition of the vocal cords, and malformation of the voice box.”
That is a good story, as described, and I'd say it points strongly to the hypothesis that this gene was a target of selection in Homo for its role in vocal development. But this gene can't be alone, and the appearance of the promoter in humans doesn't necessarily suggest a change in its vocal-specific function. I'd like to know more about the gene's variation in humans, and whether there are other functional polymorphisms of the gene in primates. Vocal anatomy is quite variable, with a few very distinctive outliers.
At the same time, let's see some expression data -- the gene probably does other stuff, too, and that might be the target of selection.