Lower animals, such as fish, amphibians, reptiles and birds, don't do much "thinking," but instead concern themselves with the everyday business of gathering food, eating, drinking, sleeping, reproducing and defending themselves.
These are instinctual processes [source: National Geographic]. Therefore, their brains are organized along the major centers that control these functions.
We humans perform these functions as well, and so have a "reptilian" brain built into us. That means we have the same parts of the brain found in reptiles, namely the brain stem and the cerebellum.
Ready to learn about the lower brain? We'll discuss that on the next page.