Few topics are more divisive than male circumcision. It's a ritual whose roots spread back through the ancient world, and it's still commonplace in countries with large Jewish and Muslim populations in particular. Yet the last few decades have seen growing opposition from the controversial "intactivist" movement, which likens the removal of penis foreskin—especially when the procedure is performed on infants—to mutilation.

Given the widespread disagreements, it's worth asking: Just how many dicks are circumcised worldwide?

In 2016, Brian J. Morris, Ph.D., set out to expand on leading 2007 research on male circumcision