M. Chris Fabricant, director of strategic litigation for the Innocence Project, has been on the front lines of these fights for more than a decade. In his fierce and absorbing new book, “Junk Science and the American Criminal Justice System,” Fabricant chronicles the battles he and his colleagues have fought to unravel a century of fraudulent experts and the bad court decisions that allowed them to thrive.

The age of the dubious court expert dawned with the rise of early 20th-century progressivism, a movement that, laudably, sought to stamp out political corruption and replace it with science and expertise. But the progressive fondness for expertise could at times extend into quackery — often laced with racism. Perhaps the best example is Sir Francis Galton, a Victorian-era polymath often cited as the father of fingerprint identification. Galton was a mathematician, a scientist and something of a celebrity. But he was also a believer in phrenology and eugenics (he actually coined the term) and supported the involuntary sterilization of groups he considered undesirable.

Judges have long been the gatekeepers of expertise. But judges are trained in law, not science, and these are two very different disciplines with almost contradictory objectives and methods of analysis. The law prioritizes consistency and reliability; science is…