Optimal-foraging theory and the concept of energetic efficiency have been used in archaeology for over a decade, usually to explore subsistence behavior. People, however, made choices for energy expenditure in other areas of culture, including lithic technology. It is suggested that a shift in the allocation of energy as an adaptive response to changes in social organization caused the widely noted decline in formal tool types and stone-tool refinement in the late prehistoric periods in eastern North America. Data from an Upper Mississippian village are used to demonstrate the economic use of poor-quality lithic raw material. A bipolar technique was used to produce flake blanks for triangular projectile points as well as a peculiar but common Upper Mississippian tool, the humpback biface. It is suggested that bipolar reduction and other lithic efficiency and economizing strategies are indicators of stress on the energy budgets of human populations.