Long-term food security and agricultural sustainability depend on protecting the eco-evolutionary processes that select for local adaptation in crops. Since seed systems structure how people acquire seed, institutional and social changes influence evolutionary processes within agroecosystems. Since World War II, the rise of professional breeding has bifurcated seed systems into traditional and formal systems, which has negatively affected agrobiodiversity, crop evolution, and agricultural sustainability. In traditional seed systems, farmers often save seed from plants that best provide desired qualities, selecting landrace crop varieties to adapt to local environmental conditions. In formal or centralized seed systems, farmers buy seeds bred primarily for maximizing yield under ideal conditions. When farmers source seeds externally, evolutionary processes underlying local adaptation are disrupted. Here, we argue that traditional seed systems provide important evosystem services, or the evolutionary processes resulting from the maintenance and use of genetic diversity that benefit society. We present a framework on how seed systems influence the evolutionary processes that enable local adaptation, which is necessary for sustainable agriculture. We discuss how changes in human values underlying traditional and formal seed systems can alter evolutionary processes that underlie local adaptation. We conclude that developing policies that support people in managing ecological and evolutionary processes within seed systems is needed to address current and future challenges of global food security and agricultural sustainability.