This chapter outlines two methodological approaches—cladistic analysis and comparatively neuro-anatomy—to demonstrate how the biological evolution of hominins-to-humans is still very relevant to understanding human behavior, interaction, and social organization. The creation of mega social structures and complex cultures does not, as so many have contended, obviate the effects of biology. Indeed, the building up of mega societies is driven, to a large degree, by the evolved biology of humans. The evolved genetics and biology of humans have large effects on almost all behaviors and interactions among individuals. Studying more of the biology of human interaction will, therefore, enhance the explanatory power of social psychology, and sociology more broadly.