She Has Her Mother’s Laugh: The Powers, Perversions, and Potential of Heredity by Carl Zimmer contains some interesting stuff on the history of paternity adjudication:
When faced with paternity disputes, Roman courts relied on the principle of pater est quem nuptiae demonstrant: The father is the one whom marriage points out. A married woman’s children should always be treated as her husband’s children, even if she gave birth a year after his death. In later centuries, judges sometimes followed this principle far beyond what nature could allow. In 1304, a husband who had been away from England for three years came home to find a new child in his house. He went to court to deny being the father. But the judge rejected his case, declaring “the privity between a man and his wife cannot be known.”
Judges were still deciding if children looked like their fathers well into the twentieth century. But the rise of genetics and molecular biology prompted some scientists to wonder if it might be possible to categorically establish kinship, to see the very atoms of heredity that tie families together. One of the first attempts to bring this science to court was made by the actor Charlie Chaplin. In 1942, Chaplin began an affair with an aspiring young actress from Brooklyn named Joan Barry. Chaplin treated her like a toy to be discarded. But when he eventually abandoned Barry, she did not go away quietly. Instead, she smashed the windows of his mansion and broke in one night, armed with a gun, demanding he take her back. By then, Chaplin had already moved on to another affair, this time with a teenager named Oona O’Neill. Barry responded by telling a Hollywood gossip columnist that Chaplin had seduced her and left her pregnant. In June 1943, well into Barry’s pregnancy, her mother filed a civil paternity suit against Chaplin on behalf of her unborn grandchild. She demanded $2,500 a month, plus $10,000 in prenatal costs. Soon, Chaplin was facing not just a civil suit but a criminal one as well. J. Edgar Hoover, the director of the FBI, had always found Chaplin a suspicious character; his anti-Nazism seemed to Hoover no different than Communism. Now he relished the opportunity to find some dirt on the actor. In February 1944, Chaplin was charged with violating the Mann Act by transporting Barry across state lines for immoral purposes while she was still a minor. He was also charged with conspiring with Los Angeles police to put Barry in jail for vagrancy. Gawkers and reporters packed a Los Angeles courthouse for the criminal trial, which dredged up lurid details about Chaplin and Barry’s affair. While Chaplin admitted to sleeping with Barry, other men testified that they had been with her during the same period. The jury acquitted Chaplin of all the charges, prompting cheers from around the courthouse. Next came the civil case over Chaplin’s paternity. Between the two trials, Barry had given birth to a girl she named Carol Ann. Chaplin’s lawyers came into court ready to raise the prospect that Carol Ann was the daughter of one of Barry’s lovers who had testified in the criminal case. And then they would present evidence that Carol Ann could not be Chaplin’s daughter, because she had not inherited his genes.
In the months leading up to Chaplin’s civil trial, his lawyers negotiated a deal with Barry’s team. In exchange for $25,000, Barry would agree to have herself and her baby tested for their blood types. If the rules of heredity eliminated Chaplin, she would drop her suit. The tests turned out exactly as Chaplin had hoped. Barry had type A and Carol Ann had type B. Those findings pointed to an inescapable conclusion: Carol Ann’s father, whoever he might be, had to have type B blood. Chaplin was type O. Carol Ann had thus inherited nothing from Chaplin. Yet Barry refused to drop the case. She had gotten a new lawyer, who would not abide by the deal made by her previous ones. Chaplin’s lawyers brought the blood test results to the judge to get the case thrown out of court. But blood type tests were still such a novelty in California that the state offered no legal guidance about their reliability. The judge allowed the case to proceed, and in January 1945, Chaplin was back in court. Throughout the trial, fifteen-month-old Carol Ann sat on her mother’s lap. Barry turned her daughter’s face toward the jury to allow them to gather bald eagle evidence, judging whether she looked like Chaplin or not. “Showing none of the temperament of her mother, Plaintiff Joan Berry [sic], who sobbed on her attorney’s shoulder, or Defendant Chaplin, who shouted his denials, she quietly amused herself by napping, yawning and gurgling,” a reporter for Life wrote. Chaplin’s lawyers countered the bald eagle with blood. They called a doctor to the stand to explain the blood-type results “with charts, diagrams, and elaborate explanations,” as the Associated Press reported. They introduced a report into evidence that included tests from two other doctors, one appointed by Barry’s lawyers and a neutral one. “In accordance with the well accepted laws of heredity,” the doctors declared, “the man, Charles Chaplin, cannot be the father of the child.”
To the jury, Mendel’s Law could apparently be stretched like taffy. They told the judge they were deadlocked, with seven jurors convinced that Chaplin was not the father, and five that he was. Barry’s lawyers filed a second suit. This time, they won, the jury deciding Chaplin was indeed Carol Ann’s father. The decision set off an uproar. “Unless the verdict is upset,” the Boston Herald declared, “California has in effect decided that black is white, two and two are five and up is down.” Nevertheless, Chaplin was ordered to pay $75 a week to support Carol Ann. All told, he would go on to pay her $82,000. The toll that the case took on his reputation was even greater. No one in Hollywood wanted to work with the little tramp anymore. Chaplin left Hollywood for good.
Adjusting for inflation, $82,000 in 1945 is about $1.2 million today (i.e., today’s plaintiffs can do a lot better under current California family law).
Looking at heredity across multiple generations there are some surprising results:
The geometry of this heredity has long fascinated mathematicians, and in 1999 a Yale mathematician named Joseph Chang created the first statistical model of it. He found that it has an astonishing property. If you go back far enough in the history of a human population, you reach a point in time when all the individuals who have any descendants among living people are ancestors of all living people.
When Chang developed his model in 1999, geneticists couldn’t compare it to reality. They didn’t know enough about the human genome to even guess. By 2013, they had gained the technology they needed. [Graham] Coop and his colleague Peter Ralph, a statistician at the University of Southern California, set out to estimate how living Europeans are related to people who lived on the continent hundreds or thousands of years ago. They looked at a database of genetic variants collected across Europe from 2,257 living people. They were able to match identical stretches of DNA in different people’s genomes, which they inherited from a common ancestor. Ralph and Coop identified 1.9 million chunks shared by at least two of the 2,257 people. Some of the chunks were long, meaning they came from recent common ancestors. Others were short, coming from deeper in the past. By analyzing the chunks, Coop and Ralph confirmed Chang’s study, but they also enriched it. They found, for example, that people in Turkey and England shared many fairly big chunks of DNA that they must have inherited from a common ancestor who lived less than a thousand years ago. It was statistically impossible for a single ancestor to have provided them all with all those chunks. Instead, living Europeans must have gotten them from many ancestors. In fact, the only way to account for all the shared chunks Coop and Ralph found was with Chang’s model. Everyone alive a thousand years ago who has any descendants today is an ancestor of every living person of European descent. Even further back in time, Chang and his colleagues have found, the bigger the ancestral circle becomes. Everyone who was alive five thousand years ago who has any living descendants is an ancestor of everyone alive today.
Presumably the rulers of 5,000 years ago were the ones who had the most children and therefore are most likely to have living descendants in 2019. We can thus all claim to have royal blood?