This paper is an empirically-based theoretical discussion of the nature and patterns of memory deficits in dementia of the Alzheimer type (DAT), which revolves around the interface between psychogeriatrics and evolutionary biology. There appears to be a hierarchical deterioration in DAT memory along dimensions of the phylogenetic hierarchy that will be defined as retrophylogenesis. It is suggested that DAT involves a process of retrophylogenesis because memory structures last to-evolve in phylogenesis are first to deteriorate in DAT. A new three-tiered model of memory is introduced with each tier originating in a different period of phylogenetic history: motor memory, emotional memory, and neocortical memory.