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Speech Gene Gone Batty
19 September 2007 (All day)
A gene implicated in the evolution of human language may have also helped bats make sounds of their own. Various bat species that emit high-frequency squeaks to detect prey and avoid obstacles share a high degree of variation in the FOXP2 gene, according to a new study, suggesting that genetic changes in the gene helped promote the evolution of this ability.
FOXP2 codes for a protein that seems to influence coordination between mouth movements and speech. The gene first attracted wide attention in 2001 when it was linked to speech and language disorders (ScienceNOW, 3 October 2001). A year later, researchers discovered that FOXP2 likely played a key role in the development of spoken language (ScienceNOW, 14 August 2002). Mice use the gene as well: Those without it cannot communicate using ultrasonic sounds (ScienceNOW, 21 June 2005).
Geneticist Stephen Rossiter of Queen Mary, University of London, and his colleagues wondered whether bats also rely on FOXP2. These mammals make human speech look simple: In a behavior called echolocation, a bat must coordinate its nose, mouth, ears, and larynx to emit and receive calls, all the while executing flight maneuvers guided in part by these signals. Working with Rossiter, Gang Li and Shuyi Zhang, both from East China Normal University in Shanghai, and their colleagues sequenced the entire FOXP2 gene in 13 bats from six families, including some that use echolocation and some that do not. They also looked at the gene in 23 other mammals, including the platypus, as well as in two birds and a reptile.
The researchers found twice as many changes in the bat's FOXP2 sequence as they found in all the other species combined--indicative of rapid evolution. What's more, closely related bats, with comparable ultrasonic capabilities, tended to have the same changes. These changes were not shared with more distantly related bats or bats that don't depend on echolocation. Some of the bats had the same mutation that in humans is associated with language disorders. "Our findings suggest that FOXP2 may have played a crucial role during the evolution and diversification of echolocation behavior in bats," says Rossiter.
That conclusion makes sense to Simon Fisher, a neurogeneticist at the University of Oxford in the U.K., who discovered a connection between FOXP2 mutations and speech disorders. He says that the results back the idea that speech and language evolved from ancestral vocal and motor systems that became rearranged and more sophisticated through time. Still, neurobiologist Constance Scharff of the Free University of Berlin in Germany notes that to really make the case for a role of FOXP2 in echolocation, functional studies are necessary, such as knocking out the gene.