translation.en: 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.
translation.zh: 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。