Philosophistry Wiki
Convergent Evolution of Intelligence

While intelligence is not strictly defined, we have a vague, collective definition. Science writers regularly produce rankings of intelligent species. Wikipedia also keeps inventories of cognitive features for well-known species. For example, elephants exhibit pointing, mimicry, and self-awareness. These social lists, when merged, resemble a hierarchy where the species with the most cognitive features number the least, whereas the species with the least cognitive features number the most.

Note: without human intervention, wolves (which evolved into dogs) would likely be Tier 3.