Since Darwin proposed universal common ancestry (UCA) More than 150 years ago, the theory, though well supported, has remained beyond the scope of formal testing. But the author of a new letter in Nature says that the famous theory that underpins modern evolutionary biology has finally passed the first large scale quantitative hurdle.

Darwin proposed that, "all the organic beings which have ever lived on this earth have descended from some one primordial form." Over the last century and a half, qualitative evidence for this theory has steadily grown, in the numerous, surprising transitional forms found in the fossil record, for example, and in the identification of sweeping fundamental biological similarities at the molecular level.