If constant or decreasing returns to scale characterize production of all commodities, then increasing only one of the inputs by a given percentage, e.g., 10 percent, will result in output rising by less than 10 percent. If the input in question is labor (population), then a 10 percent increase in labor will lead to a less than 10 percent increase in income, and per capita income [income/labor (population)] will decline since the numerator is growing less rapidly than the denominator (see Concept Box 1). If there were increasing returns to scale at least partly because of increasing marginal productivity of labor, then clearly per capita income could rise with an increase in the labor force. However, if the normal diminishing marginal productivity of labor exists, even with increasing returns to scale, per capita income will still fall with growth in the labor force because other factors of production are being held constant.