 The theory of the Neomammalian brain is based off Paul Donald MacLeans vast research conducted through comparing the structural differences between human brains and other organisms including monkeys, and a range of reptiles.MacLean's research was built upon previous neuroscientist researchers findings, including Dr James Papez, which led to the formulation of the Triune Theory of the Human Brain and the limbic system, the two major contributions that MacLean made to the faculty of neuroscience.Paul Donald MacLean was an American physician and neuroscientist that was born in Phelps, New York on May 1, 1913 into a Presbyterian minister's family, thus, ultimately becoming a religious man himself.