ABSTRACT
The introduction to this chapter reviews metaphors used to describe organismal evolution, considers the problems that gene transfer might create for the concept of lineage, and defines terms frequently used in evolutionary biology (most recent common ancestors, roots, and stem groups). The main part presents two different approaches on how the root tree of life (ancient gene duplications and analysis of shared primitive characters reconstructed for internal nodes of the tree of life), discusses the progenote concept and the Darwinian threshold, and concludes with the discussion of properties of the last universal common cellular ancestor and problems frequently encountered in inferring these properties.
