Credit: Dave Casey
From the JUNE/JULY issue of Seed:
I've recently considered a new twist on an old idea, involving human language evolution, mirror neurons and birds.
Mirror neuron studies provide intriguing evidence, although no solid proof, for gestural origins of speech. The "mirror neuron hypothesis," proposed by Michael Arbib and his colleagues, suggests that only a small reorganization of the nonhuman primate brain created the wiring that underlies speech acquisition. Missing from the hypothesis is how language (syntax) developed from speech. This is where birds come in.
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Two groups of songbirds exist: oscines, who learn their songs, and suboscines, who have a limited number of innately-specified songs. The former have well-defined neural architectures and mechanisms for song acquisition; the latter have brain structures for producing, but not learning, song. Like nonhuman primates, suboscines often use "gestures" to amplify the meaning of their utterances. And, like human children learning language, oscines need to hear, babble and practice songs before mastering them. Unlike suboscines, they learn a complex vocal syntax, analogous (though not homologous) to that of human language.
No one knows if any birds have mirror neurons or how these neurons could function, but I predict that in oscines such neurons exist and have a robust role in song development, and that only more primitive mirror neurons occur in suboscines.
Now, what about the so-called missing link between learned and unlearned vocal behavior? No one has found it in primates. But Donald Kroodsma studies a flycatcher (supposedly a suboscine) that learns its song; the song is simple, but varies among groups of birds like a dialect. I predict that these flycatchers have mirror neurons that function somewhere between those of oscines and suboscines, and will provide a model for the missing link between nonhuman primate and human communication.
—Irene Pepperberg studies animal cognition at Brandeis and Harvard. She is well known for her studies with Alex, an African gray parrot.