The preconditions for declines in this variable were memorably summarized by Ansley Coale in the dictum “ready, willing, and able.” In Gregory Clark’s Malthusian model, an upwards-sloping curve representing this variable appears on the top of two graphs. This variable can fall when quality dominates quantity in a trade-off introduced by Gary Becker. A fall in this variable (-5[1])made France the first country to undergo a historical “transition” that universally accompanies economic development. When this variable is low, an “inverted pyramid” (10[1])shape (10[1])is generated on a common (10[1])plot (10[1])that shows age on the y-axis. South Korea falls far below the “replacement rate” of this variable at around 2.1. For 10 points, name this variable that was sharply reduced by China’s one-child policy. ■END■ (10[1])