We now know that all extant living creatures derive from a single common ancestor, called LUCA, the Last Universal Common Ancestor. It's hard to think of a more unifying view of life. All living creatures are linked to a single-celled creature, the root to the complex-branching tree of life. (...) They are able to trace LUCA to a simple prokaryotic creature (a single-celled bacterium with unprotected genetic material) that lived some 3 billion years ago. It must have been a very tough organism, able to survive in very extreme environments.