Human nature can be better understood by looking to the origins of multicellular organisms about 1,000 million years ago. Even this billion-year perspective may not be enough given that multicellular life emerged from more than three billion years of evolving modes of molecular replication and single-cell evolution. 

How does human individual difference come about? Two factors contribute: variation in our genetic endowment and experiential knowledge acquired through our multifaceted, prodigiously extensive learning capacities. Genes, through the process of evolution, have invented capacities to learn. We have been invented by the processes, forces, and chance happenings of evolution through the action of genes. 

Emotion and the behavior driven by its' many forms have proven to be more difficult to study than cognitive processes because emotion is not so easily or precisely put into words. Being less well understood, emotional capacities have been underestimated as prime movers underlying decision making behavior central to human nature. Humans may be the most rational creatures on the planet, but their decision-making is nevertheless fundamentally grounded in emotion.

 In Emotion and Human Nature, Michael Breton examines the neurobiological foundations of animal and human emotion. A mathematical model of individual emotional variation is presented that is able to account for rare behavioral tendencies, both evil and altruistic. Human destiny is in the emotional makeup of ourselves, and secondarily in our rational abilities.