 The tissue that the human brain is made up of decomposes once the organism has died, so old brain tissue cannot be analysed, however, due to the large percentage that the neomammalian brain takes up in the human brain, estimated to be 76%, comparative anatomy shows that the Homo Sapien has a much larger cranial size then early primate ancestors.It must be noted that many neuroscientists believe that MacLean's theory of the Triune Theory is false, however, what is a mutual agreement between the majority of neuroscientists, is that the features that McLean has described of the neomammalian brain is the reason as to why humans have such a high-level order of thinking.Through comparing the three different sections of MacLean's Triune Theory, neuroscientists have been able to account for the complexity of the human brain in comparison to reptiles, birds and other lower order mammals.