Like physicists seeking a unified theory of the universe, biologists pine for a single family tree showing the evolutionary links among all life on earth. And, suddenly, the quest seems less quixotic. Researchers at UC Davis and elsewhere have taken advantage of quantum leaps in computing power, Internet access, molecular data and scientific interest to build elaborate databases reconstructing evolutionary relationships, known as phylogenies, and to make them freely available on the World Wide Web for further study. These databases contain hundreds of smaller trees that show the relationships among groups of species as broad as all mammals or as narrow as a single genus of sunflowers. Michael Sanderson, an assistant professor of evolution and ecology at UC Davis, and Michael Donoghue, director of the Harvard University Herbaria, planted TreeBASE on the Web this year at http://phylogeny.harvard.edu/treebase. So far, the researchers have entered data for 400 trees from about 150 studies. These are mostly green plants because of the researchers' botany backgrounds. "We have hundreds of relatively small subtrees," says Sanderson. "Presumably, one true tree links them all together. We've been working on ways to get to that one tree."