Fig. 4From: Teaching Tree-Thinking to Undergraduate Biology StudentsTwo different examples of the universal tree of life are shown. a In the simplified version, linear descent from a common ancestor is assumed. b In the more complex version, horizontal gene transfer is common amongst prokaryotic organisms, violating the assumption of linear descent. Additionally, the complex version contains a representation of the endosymbiosis event that gave rise to the eukaryotesBack to article page