Tree showing the phylogenetic estimation of the level of lethal aggression in mammals (n = 1,024 species) using stochastic mapping. Lethal aggression increases with the intensity of the colour, from yellow to dark red. Light grey indicates the absence of lethal aggression. Mammalian ancestral nodes compared with human lethal violence are shown in red, whereas main placental lineages are marked with black nodes. The red triangle indicates the phylogenetic position of humans. The silhouettes of representative mammals (downloaded from http://www.phylopic.org) illustrate the main mammalian clades. They are licenced for use in the Public Domain without copyright, except for the silhouettes of Murinae (D. Liao), Jaculus (M. Karaka), Philander (S. Werning), Rattus (R. Groom), Molossus (Zimices), Balaenoptera (C. Hoh), Rousettus (O. Peles), Connochaetes, Redunca, and Kobus (J. A. Venter, H. H. T. Prins, D. A. Balfour and R. Slotow), that are licenced under a Creative Commons 3.0 license (http://creativecommons.org/licenses/by/3.0).