Our cat started me thinking on this when it came into our kitchen once. It jumped like us at the sudden noise when a saucepan was dropped, then walked calmly round a chair that was in its way. Is our cat just reacting, then thinking, conscious, intelligent, or what?
On the face of it, intelligence and consciousness are different things because we homo sapiens theorise about those ideas and felines don't. That does not disqualify the cat. The case is not, as Descartes proposed, 'I think, therefore I am'; in our times it's more, 'I am, therefore I think'. We don't exist because we think. We exist anyway. So does the cat.
All of us think more or less, and everyone experiences the world to some degree like an Einstein. But no one expects there to be a general ability to be the equal of Einstein. Many forms of life must have been, and still are, 'conscious' in that respect - able to exist and persist without thinking too deeply about it - but not intelligent in our human understanding of the term.
Consciousness is a principle of life. In us, it has adapted over time into the exceptionally complex property we call intelligence, and which otherwise sustains all living things in their environments on Earth.
Words should not mislead us. Consciousness and intelligence are the same thing, one an extension of the other, distinguished only because our evolved minds think and speak of them the way we do.
