This is projected to lead to a drop in the fertility rate of the world‘s population, from an average of 2.37 children per woman — 237 children from every 100 women — to 1.66, or 166 children for every 100 women.

The fertility rate must be 2 for a population to remain stable and 2.1 for it to increase, the researchers said. To keep a community the same size a mother must, on average, not only replace herself but also the baby‘s father.