That means the U.S. hovers just above the replacement birth rate of an average two children per women, while the U.S. abortion policy (one of many factors influencing the Numbers) is purely voluntary.

China's one-child policy will keep birth rates low, but as life expectancy continues to increase, so will the dependency ratio, reducing the country's potential for growth.

This large-scale rollout of birth-dose vaccination, in turn, prompted a policy change across the country.