Harvard and Yale law schools cast a long shadow over clerk hiring by the Supreme Court justices—and it's growing longer.

Based on the National Law Journal's analysis of clerk hires from 2005 to 2017, 50 percent of all Supreme Court law clerks in the past 13 years graduated from either Harvard or Yale, compared to 40 percent in a similar study 20 years ago.

While alumni and professors of No. 3 Stanford University are quick to point out that Harvard's law school has about three times as many students as Stanford, by the numbers, it's still Harvard, Yale and then everyone else.

“Some of the justices don't interview or even consider students from other schools, or don't take those students seriously even when they come from the same feeder judges, and have perfect credentials,” said Micah Schwartzman, who heads the clerkship committee for University of Virginia School of Law.

Harvard law professor Richard Lazarus insists there's a reason for Harvard's dominance: ”The students who get into this place are extraordinarily gifted. They are gifted academically. They are gifted in life experiences. That doesn't mean that there aren't students at other schools who are as good as the Harvard and Yale students. There are. But the concentration we have here is, I think, unparalleled.”

This chart ranks the top 15 law school feeders from 2005 to 2017. In the second view, drill down justice-by-justice using the legend. (Colors can be turned on or off by clicking.)

Karen Sloan and Ross Todd contributed to this reporting. Infographic by David Palmer.