The path to America’s highest court nowadays narrows at a remarkably early stage in life and narrows even further soon thereafter. As youngsters, all of the justices on today’s Supreme Court attended elite colleges: three Ivy League schools, Stanford, Georgetown, and Holy Cross. From there, they all went on to study law at Harvard or Yale (though Ruth Bader Ginsburg defected to Columbia for her final year); most then clerked for a judge in the Northeast. And from there, they advanced to the bench. On the day Samuel Alito replaced Sandra Day O’Connor, in early 2006, not only was every justice a former judge, but each had been a (1) sitting (2) federal (3) circuit-court judge at the time of his or her Supreme Court appointment.

Since then, the basic pattern has remained in place. After graduating from Princeton and then Yale Law (like Alito before her), Sonia Sotomayor spent 17 years as a judge before being tapped to be a justice. More recently, Elena Kagan, after graduating from Princeton and Harvard Law, did two early clerkships and later served as the solicitor general of the United States. (The solicitor general, while not, strictly speaking, a judge, is very similar to one: he or she has an office in the Supreme Court building, and specializes in Supreme Court oral arguments.)

To appreciate how novel this Court-replenishment pattern is, recall the greatest case of the last century: Brown v. Board of Education, decided in 1954. Apart from the rather forgettable former Senator Sherman Minton, who had sat on a federal appellate court, none of the members of the Brown Court—not Earl Warren, not Hugo Black, not Robert Jackson, not Felix Frankfurter, not William O. Douglas—had any prior experience as a federal judge.

Indeed, before John Roberts became chief justice, in late 2005, the Court had always had at least one member who had arrived without judicial experience. On this point, the biographies of America’s chief justices are particularly illustrative. From John Marshall, appointed in 1801, to Melville Fuller, who served until 1910, every one of the nation’s chief justices came to the Court with zero judicial experience. The same was true of Earl Warren, who joined the Court in 1953. Three other 20th-century chiefs—Charles Evans Hughes, Harlan Fiske Stone, and William Rehnquist—came to the Court as associate justices wholly lacking any experience as a judge.

None of this means that these various pre-Roberts chiefs were unqualified. Rather, their pre-Court credentials involved notable service outside the judiciary. For example, among the justices who decided Brown in 1954, Hugo Black, Sherman Minton, and Harold Burton all came to the Court having served in the Senate; Earl Warren had served three terms as the governor of California and in 1948 had come within a whisker of being elected vice president, as Thomas Dewey’s running mate; Robert Jackson and Tom Clark had served as U.S. attorney general, and William O. Douglas had headed up the Securities and Exchange Commission. ...