The vertebrate brain is a complex structure, and how it evolved from a simpler nervous system remains obscure. The invertebrates most closely related to vertebrates, such as sea squirts and lancelets, have very much simpler brains, and it has been widely assumed that the vertebrate brain has a uniquely vertebrate evolutionary history. But work by Christopher Lowe and colleagues now shows that the genetic program that specifies the anterior end of acorn worms — very distant relatives of vertebrates, akin to echinoderms such as starfish — is very like that of vertebrates. This means that the program for specifying the vertebrate brain started out as a more generalized routine for the development of the front end of the animal. Confusion arose because the pathways involved have been lost or highly modified in lancelets and sea squirts.
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