Self-preservation is embodied in our brain's circuitry: we seek food when hungry, warmth when cold, and sex when lusty. In the evolution of the mammalian brain, circuitry for regulating one's own survival and well-being was modified. For sociality, the important result was that the ambit of me extends to include others -- me-and-mine. Offspring, mates, and kin came to be embraced in the sphere of me-ness; we nurture them, fight off threats to them, keep them warm and safe. The brain knows these others are not me, but if I am attached to them, they fire-up me-ness circuitry, motivating other-care that resembles self-care. In some species, including humans, seeing to the well-being of others may extend, though less intensely, to include friends, business contacts or even strangers, in an ever-widening circle. Oxytocin, an ancient body-and-brain molecule, is at the hub of the intricate neural adaptations sustaining mammalian sociality. Not acting alone, oxytocin works with other hormones and neurotransmitters and structural adaptation. Among its many roles, oxytocin decreases the stress response, making possible the friendly, trusting interactions typical of life in social mammals. I can let my guard down when I know I am among trusted family and friends.
Two additional interconnected evolutionary changes are crucial for mammalian sociality/morality: first, modifications to the reptilian pain system that, when elaborated, yield the capacity to evaluate and predict what others will feel and do, and notably in humans, also what others want, see, and believe. Anticipating events painful to me-and-mine is more efficient when brains can represent others as having sensations and intentions, regardless of assorted contingencies in behavior and background conditions.
Cortical and subcortical modifications also led to a greater capacity for remembering specific events -- storing for recall the reputations of assorted others; who cannot be trusted, and who can. Second, especially owing to the expansion of the frontal brain, an enhanced capacity to learn, underscored by social pain and social pleasure, allowed acquisition of the clan's social practices, however subtle and convoluted. Increased capacity for impulse control is another feature of frontal brain expansion. Social benefits are accompanied by socials demands; we have to get along, but not put up with too much. Hence impulse control -- being aggressive or compassionate or indulgent at the right time -- is hugely advantageous.
Conscience, from this perspective, is the feltwork of powerful intuitions about what is proper and right, anchored by attachments and the urge for social life, and tuned to social practices that are learned by imitation, trial and error, and imagination. Different ecological niches will yield different ways life and this may be reflected in somewhat different ideas about birth and death, about marriage and religion. The expansion of the frontal brain was likely an evolutionary response also to the advantages of more flexible capacities for planning and for evaluating consequences of a plan. Clever problem solving, with an eye to the future well-being of me-and-mine, is part of the expanded frontal brain's social jobs. Social problem-solving, including policy-making, is probably an instance of problem-solving more generally, and draws upon the capacity, prodigious in humans, to envision consequences of a planned action. In humans, it also draws upon the capacity for improving upon current practices and technologies, moving from copper to iron, moving from divine right of kings to elected councils. Rules are not the bedrock of morality, but represent rough but useful attempts at articulating those deeper, brain-based values. Rules tend to come in when group-size expand, or when social life becomes so complex that social disagreements must be negotiated and decisions spelled out. Families may have unarticulated but closely followed practices about honesty in transactions, but for who chops the wood and who milks the cow, rules are stated to prevent squabbling. Unlike other mammals, humans have developed highly complex language, and astonishingly complex cultures. This means that our sociality, and consequently ours systems of ethical values, have become correspondingly complex.