Maclean’s Triune Brain theory does not break down neatly into 5 distinct stages of biological evolution, but the 3 major segments of the brain map neatly to the general stages of Maslow’s hierarchy. The first stage of the Meta theory maps to the Reptilian Complex. The second 2 stages of the Meta Theory map to the Paleomammalian Complex. The 4th and 5th stages of the meta theory map to the Neomammalian complex.
Figure a. (MacLean 1960) Triune Brain Theory
Reptilian Complex
The reptilian complex is the oldest part of the brain called the Basal Ganglia. It is responsible for instinctive behaviors such as aggression, dominance, territoriality, and ritual displays. Reptilian behavior is typically associated with basic instinctive survival behavior. The basic motivators are fight, fright, food, and physical sexual impulses.
Paleomammalian Complex
The Paleomammalian Complex is the middle brain chronologically and consists of the Limbic System that drives emotions. It controls reproductive, and parenting behaviors. These behaviors are mammalian behaviors, specifically social mammals that raise their own young until they can survive on their own. It is the last stage of the biological brain required for pack and tribe social behavior.
Neomammalian Complex
The Neomammalian complex consists of the Neocortex where higher-level thinking including language, abstraction, logic, planning, and perception occur. These are typically what are referred to as the differentiators between humans and mammals. It is the logical part of the brain.