<P> Paul D. MacLean, as part of his triune brain theory, hypothesized that the limbic system is older than other parts of the forebrain, and that it developed to manage circuitry attributed to the fight or flight first identified by Hans Selye in his report of the General Adaptation Syndrome in 1936 . It may be considered a part of survival adaptation, leading to what describes evolution adaptation throughout the history of species differentiation in reptiles as well as mammals (including humans). MacLean postulated that the human brain has evolved three components, that evolved successively, with more recent components developing at the top / front . These components are, respectively: </P> <Ol> <Li> The archipallium or primitive ("reptilian") brain, comprising the structures of the brain stem--medulla, pons, cerebellum, mesencephalon, the oldest basal nuclei--the globus pallidus and the olfactory bulbs . </Li> <Li> The paleopallium or intermediate ("old mammalian") brain, comprising the structures of the limbic system . </Li> <Li> The neopallium, also known as the superior or rational ("new mammalian") brain, comprises almost the whole of the hemispheres (made up of a more recent type of cortex, called neocortex) and some subcortical neuronal groups . It corresponds to the brain of the superior mammals, thus including the primates and, as a consequence, the human species . Similar development of the neocortex in mammalian species unrelated to humans and primates has also occurred, for example in cetaceans and elephants; thus the designation of "superior mammals" is not an evolutionary one, as it has occurred independently in different species . The evolution of higher degrees of intelligence is an example of convergent evolution, and is also seen in non-mammals such as birds . </Li> </Ol> <Li> The archipallium or primitive ("reptilian") brain, comprising the structures of the brain stem--medulla, pons, cerebellum, mesencephalon, the oldest basal nuclei--the globus pallidus and the olfactory bulbs . </Li> <Li> The paleopallium or intermediate ("old mammalian") brain, comprising the structures of the limbic system . </Li>

The limbic system in your brain contains your brains