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A new study may have been for (and about) the birds, but it also hints at how humans may have developed the ability to speak, potentially paving the way to one day to identifying the causes of speech deficiencies.
Duke University scientists report in PLoS ONE this week that they attempted to pinpoint regions of the brain responsible for vocal skills by studying three types of birds (parrots, hummingbirds and songbirds) capable of picking up new songs and utterances as well as birds (zebra finches and ringed turtle doves) that lack the ability. Their findings: vocal pathways are always nestled in the same areas of the brain that control body movement.
"The vocal learning system is embedded within [an] ancient pathway'" designed to handle motor function that, in birds, controls their wings and legs, says study co-author Erich Jarvis, an associate professor of neurobiology at Duke University. So how did some birds develop an ability to learn new sounds? Jarvis speculates that the ability evolved from motor function or, more specifically, that the original "wiring" in the pathway linked to limbs may have duplicated and connected to vocal organs in these birds.
He believes that human language pathways may have developed in a similar fashion, given that our ability to speak is based on controlling movements in the larynx (voice box).
U.S. National Institutes of Health director Elias Zerhouni hailed the finding, noting that it "offers unexpected insights on the origins of spoken language and could open up new approaches to understanding vocalization disorders in humans."
Most birds make sounds, be it chirping, cooing, quacking, clucking, singing or even speaking. The question is why can some learn new sounds, whereas others are condemned to simply repeating preprogrammed fare. In a 2000 study, Jarvis and his team discovered that the more vocally adept birds have seven small brain areas that are not present in their preprogrammed peers. Now, they have found that brain areas around these vocal learning centers become active when the birds flap their wings or hop around. (Movement elicited the same response in these areas in the other birds; they just did not have the vocal learning centers.)
Jarvis says the new study "points us more firmly in a direction that vocal learning ability is functioning in a specialized motor system. … It doesn't conclusively solve it, but it strongly suggests it."
Constance Scharff, an animal behavior professor at the Freie Universität Berlin agrees that the new evidence is compelling. "The cautionary note is, of course, that the proximity of motor areas to song control regions, per se, does not prove anything," she says.
Interestingly, research published last week in Current Biology made a similar connection between physical movement and vocal skills in mice. In that study, rodents engineered to have a mutation to the gene FOXP2 (known to cause problems with controlling the formation of words in humans) had trouble running on a treadmill.
"I think this is a compelling hypothesis that is gaining ground from studies across different species and diverse approaches," says Simon Fisher, a professor of molecular neuroscience at the University of Oxford and co-author of the mouse study.