My own pet theory is that consciousness is an emergent property of complex systems: any complex system.
Thanks! I am really fascinated with this particular line of thinking this week.
Eve Moran

This is what Integrated Information Theory does: define what kind of system gives rise to (or better, is associated to) consciousness. And by this bottom-up, axiomatic definition, yes it could be any kind of system that has the given properties, plants, machines, systems of atoms, planets?

An interesting aspect of integrated information theory is that to determine whether something is conscious you would have to analyze its interconnectedness, and not its behavior. According to this theory you could have two systems behaving the same way, one of which has no consciousness, and one of which does. For example, it looks like the way modern computers are built they probably don’t have consciousness — but it is possible that the internet as a whole (!) has consciousness.

Another funny aspect is that by this theory you could define the minimal system with a consciousness, and exactly define what it “feels like” to be that system. In fact the minimal conscious system is made of two nodes mutually affecting each other, and this system’s consciousness can only have two states. Imagine that you can only see “all white” or “all black”, and that’s all that makes up your existence.