Why did nature bother with consciousness?
If consciousness is a view of the world that is qualitatively and spatiotemporally differentiated, it services the requirements of the individual to act in a manner that benefits its qualitatively and spatiotemporally differentiated experience of that world. i.e., it exists and acts for its individual's self.
@smcder: “Emergence seems to say that thoughts arise from the (physical) actions of the brain but then take on a causal power of their own and then work back downward to have physical effects.”
The problem, as I see it, concerns causation.
You say “thoughts arise from... physical actions...” i.e. “Physical actions cause thoughts”
You see what you have done? You have jumped from ‘material physicalism’ to the ephemeral notion of ‘thought’, and assumed that there is a direct connection from one to the other in mechanistic causal terms.
Ditch the idea that anything causes anything i.e. ditch ‘cause and effect’.
Instead, think of it like this: any effect is a form of action by an entity which is determined by the nature of its dynamic construction. As such, its actions mean something about its construction and what kind of meaning is placed on the interactive cause that incites the action.
Then, you have to think as follows: there are different classes of construction that determine different classes of meaning from interactive engagement. The meaning they derive from environmental interaction is of a specific class… it is still physical, but not of the physical class that material physicalism accounts for.
Think of there being layers of physicalism (or layers of physical realms) that are detached from one another. What detaches them from each other is the kind of meaning certain physical mechanisms derive from environmental interaction.
If an environmental event instigates a meaningful correspondence of a particular mental kind, then that mental mechanism will generate an effect that relates to mental-type meanings. Those meanings may, for example, qualify the nature of our existential being. The process of our existing, as instructed by the mental-type meanings, will be what determines (or qualifies) our actions of a mental kind—they are the actions of the existential being. There is no overdetermination because the mental actions that ensue, relate to what those actions mean in mentalistic terms only, not in microphysical terms. I act on the world in my response to what the world means to me, and those acts are of a kind that relate to the nature of my particular meaningful correspondence.
Downward causal consequences are incidental to the meaning behind the actions and the consequence of those actions in that class of meaning about the world.