Here's a new development in the search I described last week for the genes that make us uniquely human. Science's Michael Balter reports on a new study about a gene that's crucial for making big brains. Mutant versions of the gene produce people with tiny brains--about the size that Lucy had 3.5 million years ago. Comparisons of the human version of the gene with other mammals shows that it has undergone intense natural selection in our own lineage. Size is far from everything, however. While humans have huge brains compared to other mammals, new kinds of wiring may have been more important in the transformation of the hominid brain into something that could be called truly human.