Short answer: no other creature has developed complex languages, written books or made art. Long answer: there is a plausible argument that consciousness might

Short answer: no other creature has developed complex languages, written books or made art. Long answer: there is a plausible argument that consciousness might be a gradient. Certain creatures might express some level of meta consciousness, yet still far from what humans can do. For instance, elephants, primates or even just a dog might express some sort of empathy or more subtle mental states that do not equate with the experience itself, which would be mere phenomenal consciousness, but they do not appear to articulate to themselves those mental states and do anything more than simple reactions with those states. Ultimately the claim comes from empirical observations: there's an immense evolutionary gap between humans and everything else, so that we can plausibly claim that we are the only fully meta-conscious creatures.