What Is the Difference Between the Brain and the Liver?

Why do some creatures and organisms need brains for example and why do other creatures not? I think the reason would probably lie in evolution obviously. One interesting question is what's the difference between the brain and the liver? Is this the presence of these very long slender connections like the wires on the circuit board or the communication channels in some information processing device? It speaks to an interesting proposition if it is the case that the structure of the brain recapitulates or installs causal structure in the world. That kind of suggests that the brain is trying to explain a world in which there is action at a distance.