It seems to me that splitting life into "primitive" and "non-primitive" or "intelligent" and "non-intelligent" groups is a rather anthropocentric view. Just because we consider ourselves the crown of evolution or creation (as you like), doesn't mean that oversized brains are necessarily a good idea when it comes to survival, and that life would naturally tend towards developing "intelligence". Simplicity and large numbers may turn out to be a far better strategy in that respect. Viruses and microorganisms will probably roam the earth long after humans are a distant history. Plus, their simplicity and robustness makes them far better interstellar travelers than we can ever hope to be. Viruses may be busy colonising the galaxy as we speak, while we are stuck on this planet, trying to keep our brains occupied with musings about god, the universe and everything ...