Figure 1.

Phylogenetic tree of the major animal clades, giving a summary of the current evidence for true individual recognition (IR) and private self-awareness (PrSA). Arrows indicate where public self-awareness (PuSA) and PrSA supposedly evolved, depending on which hypothesis applies. The tree itself is based on Tudge [37]. Examples of references: familiarity [38] in Reptilia, true IR [39] and PrSA [14,15] in Aves, true IR [40] and PrSA [7,12,13] in Mammalia, familiarity (?) [41] in Amphibia, true IR [42,43] and PrSA [17,33,34] in Actinopterygii, familiality [44] in Chondrichthyes, true IR (?) [45] in Mollusca, true IR [46,47] in Arthropoda.