One of the amazing claims of modern biology is that all life on Earth is descended from one common ancestor, a one-celled microbe that appeared 4 billion years ago. As ages passed, this tiny organism multiplied, differentiated and evolved into the enormous array of species that have since populated the Earth.

Scientists say this huge genealogical chart will have practical benefits for medicine, agriculture and the environment, as well as providing a basic understanding of life on our planet. They say it will be as valuable as the chemists' familiar Periodic Table of the Elements, only much larger and more complex.

A better source of Taxol, the breast-cancer drug, was discovered by tracing the genetic relationship between Taxol's original source, a rare yew tree, and a more common shrub.