We're talking psychology, there is no proof and the only evidence is explanatory power.
1. first evolved sense and response. This is the most basic part of consciousness, and is found in almost all life. Things from bacteria to plants to animals sense their environments and react to them.
2. Next came synthesis- the brain. Vertebrates and many other animals have nervous systems that gather sense data in a brain which processes it as a synthetic reality to which the body responds. The body continues to sense and react to signals not gathered in the brain as well. The animal isn't aware of the sensations, it is just the first stage in approaching awareness.
3. Conditioning. The animal lacks memories as we experience them, but the brain stores information and reacts to it unconsciously via conditioning. This is found in insects and most animals with brains.
4. Memory. This is conditioning such that the animal remembers specific information and physiological states associated with that information, it moves beyond conditioning in that the memory may be available even when the environmental triggers to it are not. This is found in most higher vertebrates. Birds and mammals tend to have memories.
5. Symbolic memory. The animal symbolizes remembered data and then manipulates those symbols. This is found in higher birds and mammals that use tools and solve problems they haven't encountered before without trial and error. It's also the basis for learned behaviors.
6. Symbolic memory and reality synthesis containing a symbol for self. This is the inclusion of the self in the synthetic reality, seeing oneself as a causative agent in that reality. This is consciousness. It is only known to exist in animals that recognize themselves, of which very few exist.
now the problem is that all of these parts of consciousness evolved at different stages in animals, and one or more of them doesn't indicate consciousness. They must ALL be present for an animal to be conscious.