Parrot sings Mozart. If this parrot singing the Queen of the Night's great aria from The Magic Flute does not blow your mind, your mind is unblowable. (Thanks to Celinafink who uploaded this video to YouTube.)
Although our closest genetic kin in the animal kingdom are the apes, our closest functional relatives are birds. We've been seeing individual details supporting this conclusion for some time on Babel's Dawn, and now a paper has appeared in Nature Reviews|Neuroscience that pulls together the "astonishing cognitive, neural and molecular parallels" [p.747] matching humans with birds. For the past six million years our lineage has been moving steadily away from the other apes and following a convergent path that birds took much earlier. Then we began to build something on the bird foundation that birds never managed… unless some of them did.
Birds learn to sing their songs and babies learn to make the sounds of their language in the same way. That way is "a combination of predispositions and learning,"  ways that sound vague but match up nicely. The predispositions in both cases are biases toward the sounds of their conspecifics. Human babies are much more interested in human voices than they are in other noises. Young songbirds are much more interested in the songs of their own species than in the songs of other kinds of birds. If you raise a bird so that it hears the song of its own kind and the song of another bird, it will learn its own kind's song.
Most of us probably have seen examples of babies responding to the human voice in some strong way. I have also seen it in birds. Once I found myself trying to help a very young African swallow. Not surprisingly, it was deeply downcast to find itself in my clutches, but it perked up right away when it heard some fellow swallows (not its parents) screetching.
This interest in one's own kind's vocalizations is important to making these sounds easier to remember and imitate. There are stories of autistic children becoming interested in mechanical noises and being able to do remarkable imitations of different kinds of automobiles. It is amazing, but dreadful. The children have become fixed on the wrong thing, like Konrad Lorenz's goslings that followed him around instead of their mother.
Birds in the lab have been raised in isolation, unable to hear what song they should be making; even so they eventually make some kind of sound that "retains certain species-specific features"  This, of course, is a forbidden experiment to perform on humans, but it sometimes happens that owing to monstrous parents or circumstances a child is raised in isolation. These children, when found, are without language, but they are not mute. They make sounds with human features. Children born profoundly deaf are also not mute, even though they may never speak. They too make human sounds.
Furthermore, both birds and humans go through a period when learning is best accomplished. This sensitive period ends in early adolescence for humans, after which point it becomes difficult to learn a language with imposing an accent. The sensitive period in birds of course is much shorter and varies from species to species.
The learning itself consists of a series of shared phases, beginning with listening. Early vocalizations are not very close to what their older models produce. In humans these preliminary vocalizations are called babbling, in birds they are called subsong. With practice comes improvement and finally bird and human make the sounds typical of their kind.
The similarities between bird and baby learning have been recognized for centuries, but there is also an old phrase, bird brained, that denigrates some humans by denigrating the brains of all birds. So it has been quite surprising to learn that the brain architecture supporting babbling and birdsong is similar. The bibliography lists a "landmark paper [published in 2004 and claiming 28 authors] presenting a complete overhaul of the nomenclature of the avian brain, indicating possible homologies with the brain of mammals, including humans."
"Songbirds have specialized, discrete brain regions for song recognition, production and learning" . The Nature Reviews paper also includes this astonishing sentence, "both the LMAN and HVC [regions of the songbird's brain] have been tentatively suggested to correspond functionally to Broca's area [the region of the human brain involved in speech production]" . I am familiar with Broca's area and Wernicke's area (involved in speech production) in the human brain, but, come to think of it, I do not know of a specialized language learning area. The authors suggest that the region devoted to listening to sounds during the human babbling stage is the "superior temporal cortex," a region not far from Broca's area, but none the less distinct from it.
An important difference between avian and human brains is that the avian parts seem more fully specialized for song. Human brains tend to overlap vocalization and perception functions, a fact that should surprise no regular reader on this blog. This difference likely comes out of the difference between birdsongs and speech. Birds sing the same song in predictable situations. Even so, it appears that both groups have specialized parts of the brain for early listening to what they need to know. They also have an area that compares their own output with what they hear produced by their elders, and a third area that controls the muscles and tissue supporting vocalization.
Songbird brains are a small fraction of our own proud bolder and that weeness does limit what they can master, but they are much more agile minded than was supposed just a few years ago.
The biggest surprise in the past decade since the Doupe-Kuhl paper first linked birdsong and speech, has been the discovery that the same mutated gene, FOXP2, is implicated in both cases. This finding has been part of the larger revolution in genetic understanding that has gone on ever since the full human genome was obtained. That feat was so decisive that already it seems like a strange dream when I recall the controversy that took place over whether the project was the proper thing for scientists to do. FOXP2 in humans appears to be related to the development of brain areas that "play important parts in motor functioning and auditory pathways connected to speech" . "Structural and functional imaging of humans with FOXP2 mutations show subtle volume differences and striking activation differences during language tasks."
In birds, FOXP2 appears to be active in the bird's AFP circuit which is crucial to song learning. I await the discovery of what FOXP2 is up to in the humpbacked whale.
Taken as a whole, this information suggests that after the human lineage separated from the chimpanzee/bonobo line we began vocalizing in ways that other apes don't. That process led to a convergence with processes discovered millions of years earlier by songbirds, including the way to sort out the brain regions and the use of FOXP2. At some point, however, we added a meaningful role to our vocalizations and they began to take on characteristics not found among the birds. It may be that in our evolutionary story there is a distinct bird phase. We did not fly, but we sang charming songs without meaning. Indeed, sometimes we still do. Falalalala-lala-lala.