Figure11-5Common Marginal and Average Product of Labour Curves More realistic marginal product and average product of labour curves look like inverted U-shapes. Starting from a very low input level, the marginal product often rises as the firm employs more of the variable input. That’s because hiring additional workers allows greater specialization of their tasks and leads to increasing returns. Once specialization is exhausted, however, diminishing returns to additional workers set in and the marginal product falls. In addition, the average product of labour rises when marginal product exceeds average product, while the average product falls when marginal product is less than average product.