I believe brains evolved from an unmyelinated state to a myelinated state.
Since this did involve an additional investment of biological energy, myelin
is almost certainly an evolutionary advantage.
--
sentience@pobox.com Eliezer S. Yudkowsky
http://tezcat.com/~eliezer/singularity.html
http://tezcat.com/~eliezer/algernon.html
Disclaimer: Unless otherwise specified, I'm not telling you
everything I think I know.