Two studies published this week point to genes that might optimize size in parts of the nervous system. On page 365, researchers describe the effects of a ubiquitous protein called b-catenin on the size of the brain9s cerebral cortex. And in a paper published online this week by Science, another team explains how a protein called Six6 interacts with key cell-division genes to control the size of the developing retina and pituitary gland.