Why? Having dabbled a bit in evolutionary simulations, I find that, once you have unicellular organisms, the emergence of cooperation between them is only a matter of time, and from there multicellulars form and cell specialization based on division of labor begins. Once you have a dedicated organism-wide communication subsystem, why would it be unlikely for a centralized command structure to evolve?
On Earth multicellularity arose independently several dozen times but AFAIK only animals have anything like a central nervous system.
If animal-complexity CNS is your criteria, then humans + octopuses would be a counterexample, as urbilaterals wouldn’t be expected to have such a system, and the octopus intelligence has formed separately.
The last common ancestor of humans and octopuses probably didn’t have a very complicated nervous system, but it probably did have a nervous system: most likely a simple lateral cord with ganglia, like some modern wormlike animals. That seems to meet the criteria for shminux’s “dedicated organism-wide communication subsystem”.
On Earth multicellularity arose independently several dozen times but AFAIK only animals have anything like a central nervous system.
If animal-complexity CNS is your criteria, then humans + octopuses would be a counterexample, as urbilaterals wouldn’t be expected to have such a system, and the octopus intelligence has formed separately.
The last common ancestor of humans and octopuses probably didn’t have a very complicated nervous system, but it probably did have a nervous system: most likely a simple lateral cord with ganglia, like some modern wormlike animals. That seems to meet the criteria for shminux’s “dedicated organism-wide communication subsystem”.