The origin of life and the last universal common ancestor: do we need a change of perspective?

A complete tree with roots, trunk and crown remains an appropriate model to represent all steps of life's development, from the emergence of a unique genetic code up to the last universal common ancestor and its further radiation. Catalytic closure of a mixture of prebiotic polymers is a heuristic alternative to the RNA world. Conjectures about emergence of life in an infinite multiverse should not confuse probability with possibility. (C) 2009 Elsevier Masson SAS. All rights reserved.