The Wages Fund theory developed by Adam Smith and later expanded by Karl Marx and David Ricardo states that the total wages paid to laborers is fixed, or determined by the total capital invested in wages. As the labor supply increases, the average wages will decrease as the fixed wages fund is divided among more workers. The theory also argues that average wages will decline with increases in population and rise as the wages fund is enlarged or the labor supply decreases. However, the theory does not adequately explain variations in wages between different levels, regions, or account for differences in worker efficiency.