When the sea squirt is born it has eyes, a brain, and a tail. It needs these tools to swim around and find an appropriate host to live off of. Once a host is found the squirt eats its own brain and turns into a plant-like parasite. In its new secure condition the brain is no longer needed for survival. It’s only remaining utility is therefore to provide nutrition.

We are descended from this creature. No matter how we romanticize our existence we are essentially biological agents whose only purpose is to survive and reproduce. We have a brain only because it serves that purpose.