A number of scholars point out that a fragmentary resource-based perspective was evident from the 1930s, noting that Barney was heavily influenced by Wernerfelt's earlier work which introduced the idea of resource position barriers being roughly analogous to entry barriers in the positioning school. Other scholars suggest that the resource-based view represents a new paradigm, albeit with roots in "Ricardian and Penrosian economic theories according to which firms can earn sustainable supranormal returns if, and only if, they have superior resources and those resources are protected by some form of isolating mechanism precluding their diffusion throughout the industry." While its exact influence is debated, Edith Penrose's 1959 book "The Theory of the Growth of the Firm" is held by two scholars of strategy to state many concepts that would later influence the modern, resource-based theory of the firm.