In recent years, there’s been a significant political and cultural push to open up combat occupational specialties in the nation’s military to female service members. The rallying cry for equality has not been without critics, of course; many have accused the various branches of yielding to political pressure by easing the physical requirements of some jobs in order to meet society’s demand for a mixed-gender combat force. As the debate continues to rage, one facet of service has remained noticeably untouched, however: the nation’s Selective Service System.

In the United States, nearly all male citizens are required to register with Selective Service within 30 days of their 18th birthday. Once registered, male citizens could find themselves called into involuntary service during a national crisis—a process commonly referred to as a draft. The United States has utilized a draft in a number of modern conflicts, ranging from World War II to Vietnam, making the Global War on Terror something of an exception.

In a crisis requiring a draft, men would be called in a sequence determined by random lottery number and year of birth. Then, they would be examined for mental, physical, and moral fitness by the military before being deferred or exempted from military service or inducted into the Armed Forces,” the Selective Service website states.

In recent years, the issue of women having to register with Selective Service tends to crop up in online debates about gender equality, with some pointing toward wartime casualty statistics as an example of gender inequality favoring women. Throughout history and even today, men are far more likely to die in combat than women, due in no small part to fewer women serving in the military and restrictions on the roles they’re permitted to fill when they do enter service.