Human and yeast genes go way back—about a billion years ago, humans and yeast shared a common ancestor. It turns out, we still have thousands of genes in common, says Edward Marcotte, a professor of molecular biosciences at The University of Texas at Austin. In his lab, he and scientists replaced over 400 yeast genes with human genes—and almost half of the yeast were “successfully humanized,” meaning that they functioned normally. The team’s results were published in the journal Science last week. Marcotte explains how these findings could help us better understand human gene function and mutation.