What part of the brain would have the least primitive organisms?

The part of the brain that would have the least primitive organisms is the neocortex. This region is responsible for higher-order functions such as reasoning, complex thought, and sensory perception, and is highly developed in mammals, particularly humans. In contrast, more primitive organisms primarily rely on simpler brain structures, such as the brainstem and limbic system, which govern basic survival functions and emotions. Therefore, as organisms evolve, they develop more advanced brain regions like the neocortex, leading to increased cognitive abilities.