Origins of Vertebrate Success

The News Focus article “In search of vertebrate origins: Beyond brain and bone” by Carl Zimmer (3 Mar., p. 1576) highlights recent findings of the progressive acquisition of bone and brain structures. These findings support Gans and Northcutt's theory (1), which postulates that the emergence of vertebrates was made possible by the invention of neural crest cells (embryonic cells that give rise to many peripheral tissues including the eyes, nerves, and skull), and specifically, this then led to the development of evolutionarily advantageous complex head structures. We agree with the importance of the neural crest in this regard, but wish to point out the contribution of one important neural crest derivative—the peripheral myelin sheath—to the success of the vertebrates. Without this structure, the vertebrates as we know them simply could not exist (2).