Hi everyone,
The Triune system is one of the most famous and well accepted ways of classifying the brain and its evolutionary development.
The human brain is said to consist of three systems... The Reptilian system, the Limbic system and the Neo Cortex.
The Reptilian system is responsible for aggression, dominance, territorial behavior. The Limbic system is said to be responsible for emotion, reproductive and parental behavior. The Neo Cortex is said to be responsible for language, planning abstract thinking and so on.
In evolutionary terms the first one is said to have evolved in reptiles and the second in early mammals and the Neo Cortex in higher mammals and more so in humans.
Of course, this division is not accepted today in such a clear cut manner as in earlier decades, because many organisms have been found to be exceptions to these stages of development. Also, in humans, all the three systems function in an integrated manner as one unit.
Regardless of this, the Triune system is still regarded as one of the most representative models in relation to brain development and functioning.
IMO...the Triune system shows that advanced brain development in higher mammals did not happen merely as an extension of the earlier ones but appears to have developed as separate systems with separate structures.....with a step up at each level.
Just some thoughts.
Cheers.
Sriram