Theobald says his most surprising results were "how strongly they support common ancestry." Rather than being disappointed about simply backing up a long-held assumption, he says that at least, "it's always nice to know that we're on the right track."
These findings do not mean that a universal common ancestor establishes the "tree of life" pattern for early evolutionary dynamics. Nor, however, do they infer a "web of life" structure. The tree versus web debate remains "very controversial right now in evolutionary biology," Theobald says, reluctant to pick a side himself.
One of the other big unknowns remaining is just when this universal common ancestor lived and what it might have looked like—a question that will take more than Theobald's statistical models to answer. Theobald also notes that the support for a universal common ancestor does not rule out the idea that life emerged independently more than once. If other, fully distinct lineages did emerge, however, they either went extinct or remain as yet undiscovered.
Research will likely push on into these dusky corners of early evolution, Penny notes, as "scientists are never satisfied." He expects that researchers will try to sort back even earlier, before DNA took over, and assess the early stages of evolution during the RNA days.
On a more foundational level, Penny says, the paper should not put an end to the assessment of ancestral assumptions. Instead it should be a reminder that "we have never thought of all possible hypotheses," he says. "So we should never stop considering some new approach we haven't thought of yet."
*Erratum (5/13/10): This sentence was changed after publication. It originally stated that a universal common ancestor is more than 10 times more likely.