In June 1943, Charlie Chaplin signed a stipulation: one physician he named, one the child's guardian ad litem named, and a third those two physicians would pick themselves, would draw blood from him, from Joan Berry, the young actress who said he had fathered the daughter she was carrying, and from the child once she was born. If two of the three found he was not the father, the suit would be dismissed with prejudice. The doctors tested the blood and reported, unanimously, that Chaplin could not be the father: his blood typed O, Berry's typed A, the child's typed B, and under the rule of heredity they cited, a type B blood group cannot appear in a child unless a parent carries it.
The case went to trial anyway. The child's original attorneys never filed the dismissal the stipulation called for; new counsel were substituted in, and a Los Angeles judge, Stanley Mosk, denied Chaplin's motion to dismiss on March 8, 1944, without hearing any evidence on whether the stipulation was fair to the child. At trial, the court told the jury that no statute had declared blood tests legally conclusive, so the jurors were free to weigh the doctors' findings however they liked. In April 1945 they found Chaplin was the father anyway, and he was ordered to pay $75 a week in child support and $5,000 in attorneys' fees. He appealed, and in 1946 California's Second District Court of Appeal affirmed: a guardian ad litem, it held, had no authority to sign away an unborn child's right to a trial, and in any case the panel was bound by a nine-year-old state Supreme Court precedent holding that blood-grouping evidence, however reliable, was only expert opinion, weighed like any other testimony and no more binding than a witness's say-so.
One of the three appellate judges, Marshall F. McComb, concurred in the result because precedent bound him to, and used his own opinion to explain why he thought the precedent was wrong. Legal scholars, he noted, had already called it a serious miscarriage of justice. He pointed to the courts' existing reliance on the microscope, the X-ray, and chemical tests for facts no witness could supply, and argued that blood grouping deserved the same trust.
A correct answer does not enforce itself. California law in 1945 treated a blood exclusion the same way it treated a witness's recollection, something a jury could believe or disregard. That rule did not come from the trial court or from the appellate panel that reviewed Chaplin's case; both were bound by a precedent only the state's highest court, or the Legislature, had the power to change. The biology had already settled the question. The courts bound by that precedent were not yet free to act on it.
The California Supreme Court declined to reconsider: Chaplin's petition for a hearing was denied on July 24, 1946, with only two justices, Roger Traynor and B. Rey Schauer, voting to take the case. The fix came seven years later, from the Legislature rather than the courts. A 1953 law adopting the Uniform Act on Blood Tests to Determine Paternity made a unanimous exclusion decisive in a case like his; the state's own Supreme Court later confirmed as much, while noting that the Legislature had deliberately left a separate rule in place for a child born to a married mother. A jury weighing a case like his, with no married mother's presumption to override, could no longer disregard three doctors who agreed. It lost the chance to try.