This article focuses on a way of doing theology which interfaces with the science of evolutionary psychology. Faith seeks understanding or explanation. Augustine seeks to understand the Trinity through rational psychology; Aquinas explains “Creator” in the philosophical category of Aristotle’s “Prime Mover.” On the theology of original sin, this paper seeks explanation of “original sin” from the evolution of the brain. “Original blessing” precedes original sin in creation. Each step of the evolutionary process benefits the living organism, including humans, but when the “blessing” does not follow the priorities of the next evolution’s level, it can destroy the organism. For example, sex is a beneficial instinct to perpetuate the species but, at times, it prevails destructively over individual’s rational relationship with others; traditionally, we attribute the destructive result to “original sin.” The mammalian mother-offspring bonding is an evolutionary improvement over reptilian non-relationship between the two, but, in some instances, a mammalian mother neglects the child. Again, we can attribute that neglect to original sin when, in fact, according to evolutionary integrity, the mother simply allows her reptilian indifference to prevail over the mammalian care. Original sin is not sin by itself but the pulling down by the function of the lower brain and the mismatch of our mental equipment attuned to surviving, adapting, and reproducing in a bygone era but inadequate in a fast paced present. Jesus’ vision of a new inclusive world (kingdom of peace, justice, and love) transcends the limitations of each brain (territoriality, sex, ethics of survival). The name “God” is given to “Wisdom of Nature,” or Greater Reality or Higher Purpose that we inevitably conceive in evolution. Understanding the faith from a scientific theory like evolution critiques a supernaturalistic and fatalistic religiosity; at the same time, the input of Christian revelation forestalls a purely reductionistic faith that gets stuck in the hormones!