More than 150 years ago, Darwin proposed the theory of universal common ancestry, linking all forms of life by a shared genetic heritage from single-celled microorganisms to humans. Until now, the theory that makes ladybugs, oak trees, champagne yeast and humans distant relatives has remained beyond the scope of a formal test. This week, a biochemist reports the results of the first large scale, quantitative test of the famous theory that underpins modern evolutionary biology.