In this talk we consider several proofs, old and new, of the reduction phenomenon: Many mathematical models of biological systems that incorporate dispersal and reproduction exhibit the phenomenon that increased dispersal reduces overall growth. Karlin first proved this for basic, parameterized linear discrete-time model in 1975, and many other proofs have been discovered since then. We review some of these proofs, indicate how they are connected and also provide streamlined, novel proofs of this celebrated biological principle.