This seems counterintuitive, but turns out that as infant mortality is reduced, population sizes also decrease, because parents don't need to anticipate that their babies are going to die.
听起来似乎有违常理， 但只要婴儿的死亡率降低， 人口也将减少， 因为父母们不用担心孩子会过早夭折 而生更多的孩子。