The Harrod-Domar (H-D) growth model assumes a fixed capital-output ratio, signifying absence of substitutability between capital and labor, leading to a “knife-edge” problem wherein balanced growth of capital (fixed warranted rate) and labor (fixed natural rate) occurs only by accident, preventing the attainment of macroeconomic stability with full employment. The neoclassical Solow-Swan (S-S) growth model provides an elegant solution to the H-D problem by endogenizing the warranted rate via the saving-investment relation, wherein capital growth is a function of a fully adjusting income-capital ratio (inverse of the H-D capital-output ratio)— allowing for smooth substitutability between capital and labor while keeping the natural rate exogenously fixed. The S-S model implies a positive, albeit temporary output growth effect of a higher saving rate. The present paper extends the capital-labor ratio’s influence onto the natural rate via effects on labor productivity through a modified Arrow learning by doing framework, and via labor participation through real wage adjustments. Thus, the positive output growth of a higher saving rate, although temporary in the short run as in the S-S model, is permanent in the long run through adjustments in both the warranted and natural rates—a generalization of the Solow-Swan model.