Paul MacLean, founder and long-time chief ofthe Laboratory of Brain Evolution and Behavior,National Institutes of Health, is a pioneeringfigure in the emergent field of evolutionaryneuroscience. His influence has been widelyfelt in the development of biologicalpsychiatry and has led to a considerableliterature on evolutionary approaches toclinical issues. MacLean's work is alsoenjoying a resurgence of interest in academicareas of neuroscience and evolutionarypsychology which have previously shown littleinterest or knowledge of his extensive work. This chapter builds on MacLean's work to bringtogether new insights (...) into the neuralarchitecture of human development, hierarchy,conflict behavior, and reciprocity in the formof the Conflict Systems Neurobehavioral Model. Hamilton 's rule of kinship altruism orinclusive fitness is proposed to be the gene'seye complement to MacLean's evolutionaryneuroscience and the CSN Model derivedtherefrom. Hierarchy, conflict behavior andreciprocity are also central issues in healthydevelopment as well as in clinical syndromes ofdepression, mania, and other socialmaladjustments. The emerging insights permitthe integration of the concept of inclusivefitness underpinning evolutionary psychologywith MacLean's perspective on evolutionaryneuroscience as well as the definition of newchallenges for mental health and socialstability. The policy implications areindicated. (shrink)