The vast majority of creatures do not have an awareness of self, and therefore are incapable of deluding themselves. Those few that do possess self-awareness (e.g., apes, dolphins, elephants) do not possess sufficient mental acuity to engage in serious self-deception. Observers have documented numerous instances of chimpanzees employing sophisticated subterfuge in their social interactions, but they do not appear to turn this behaviour inward. Only humans, endowed with a hyperactive (and, in some cases, riotous) imagination, can fool themselves.
– Leonard Shlain, Sex, Time, and Power: How Women’s Sexuality Shaped Human Evolution (2003)