This chapter describes three theoretical analyses which shed light on the question as to what was different about the behavior, morphology, or circumstances of our ancestors that allowed our technology and culture to take off in such an extraordinary manner. Here, mathematical modeling has proven extremely insightful, particularly by demonstrating that high-fidelity transmission would lead to cultural traits persisting for extremely long periods. The theoretical findings supported a verbal argument that had been made previously by psychologist Michael Tomasello at the Max Planck Institute for Evolutionary Anthropology in Leipzig. Tomasello had proposed that our species' unique capabilities for language, teaching, and efficient imitation had allowed us to transmit knowledge with a higher fidelity than observed in other animals, and that this transmission fidelity explained the existence of cumulative culture (what he termed “ratcheting”) in humans, but not in other animals. The chapter ends with an account of an experimental investigation in children, chimpanzees, and capuchin monkeys that reinforces these theoretical findings.