FoxP2 in song-learning birds and vocal-learning mammals

FoxP2 is the first identified gene that is specifically involved in speech and language development in humans. Population genetic studies of FoxP2 revealed a selective sweep in recent human history associated with two amino acid substitutions in exon 7. Avian song learning and human language acquisition share many behavioral and neurological similarities. To determine whether FoxP2 plays a similar role in song-learning birds, we sequenced exon 7 of FoxP2 in multiple song-learning and nonlearning birds. We show extreme conservation of FoxP2 sequences in birds, including unusually low rates of synonymous substitutions. However, no amino acid substitutions are shared between the song-learning birds and humans. Furthermore, sequences from vocal-learning whales, dolphins, and bats do not share the human-unique substitutions. While FoxP2 appears to be under strong functional constraints in mammals and birds, we find no evidence for its role during the evolution of vocal learning in nonhuman animals as in humans. FoxP2 is a member of the winged helix/forkhead class of transcription factors (Lai et al. 2001; Shu et al. 2001). It is expressed in multiple fetal and adult tissues, with a high expression in certain regions of the fetal brain (Lai et al. 2001; Shu et al. 2001). Mutations in the gene cause severe deficits i