"the back and center part of our brains, containing the brain stem, cerebellum, and basal ganglia, are almost identical to the brains of reptiles. Known as the "reptilian brain," these are the oldest structures of the brain, governing basic animal functions such as balance, breathing, digestion, heartbeat, and blood pressure. They also control behaviors such as fighting, hunting, mating, and territoriality, which are necessary for survival and reproduction. The reptilian brain can be traced back about 500 million years. (See Figure 3.)"