即使人工智能在一些圈子里引发了高涨的乐观情绪，但人口对全球未来经济仍存在巨大的不确定性影响。In 2000 the world’s fertility rate was 2.7 births per woman， comfortably above the “replacement rate” of 2.1， at which a population is stable. Today it is 2.3 and falling.
