An interesting article published in Nature about FoxP2 (Forkhead box protein 2) gene, which has been shown to be critical for learning speech. Discovered first in a British family with inherited speech problems, foxp2 has been shown to have two amino acid differences in the human form when compared to chimpanzees. The human version, when inserted into mice, makes the mice vocalize differently (but not speak, obviously). Interestingly, neanderthals had the human form of the gene, another piece of evidence in support of the idea that neanderthals could speak.
But the function of foxp2 in the brain seems to be much broader than simply speech. In the Nature article, the researchers show that mice with the human version of foxp2 are also smarter and able to solve mazes faster than mice with their own version of foxp2. It seems that foxp2 may be important for neural plasticity.