Mary-Claire King, the scientist who discovered that God is a woman

The Grandmothers of the Plaza de Mayo gave genetics the opportunity to repay a debt to human rights. After a dark past throughout the 20th century, in which it was used to develop eugenics, justify racism, and commit genocide, the Grandmothers allowed this science to reclaim its rights. “Genetics is a tool, and like any tool, it can be used for good or evil. A hammer can be used to build or to kill,” geneticist Mary-Claire King , the newly awarded Princess of Asturias Award for Science, explained to me a few years ago.

This is how she used that hammer: “We use genetics to build indestructible homes that would allow the return of stolen children.” King shared those phrases with me for a report on the grandparent index , the innovative instrument she developed when the Argentine Grandmothers knocked on the door of science in search of a solution to their problem: proving that a child was their grandchild, kidnapped by the dictatorship's repressive apparatus, while their mothers remained missing.

In the 1980s, before the development of modern DNA testing, this challenge was far more complex than a paternity test. “The biggest scientific problem the Grandmothers faced—and, therefore, me as well—was how to obtain definitive proof of a child's identity when both parents were missing and presumed dead,” argued the geneticist, who is still involved in the cause of grandchildren and human rights around the world.

After much effort, and with the help of other prominent geneticists, he concluded that the best tool available was mitochondrial DNA sequencing, which in 1985 was done by hand, “without any automation.” And although the process was slow, the results were “extremely informative.” King explained it this way: “Mitochondrial DNA is inherited solely from the mother, so every son or daughter has exactly the same mitochondrial DNA sequence as their mother. Therefore, a maternal grandmother, maternal aunt, or maternal cousin—any relative linked exclusively through the maternal line—could provide matching evidence to confirm a child’s identity.”

The Grandmothers were fascinated by the existence of a secret thread that connected us to our mothers; King recalls that they joked that mitochondrial DNA was proof that God was a woman, that he had placed those chromosomes there to help them. It was an invisible trace that the oppressors hadn't counted on, and it completely thwarted their plans. It wasn't enough to kill the mothers and erase all traces of the baby's birth: science had cornered them.

King's work brought down many more criminals by laying the groundwork for identifying victims of dictatorships, wars, and genocides across the globe: from the Balkans to Haiti, from Rwanda to the Philippines.

But the story of the geneticist in Argentina has more morals. The final lesson, one we are learning simultaneously in different parts of the world, is that it is not wise to let our guard down in the face of history. Javier Milei's government has clipped the wings of the National Genetic Data Bank—an essential body for harnessing King's science—by decree, seriously jeopardizing the continued discovery of babies stolen by the dictatorship. So far, 139 people have been found. No less than 139 lives recovered; 139 sinister crimes foiled.

Another, more interested, interpretation is to vindicate the role that scientific journalism—my profession—can play in the most critical moments. The Grandmothers turned to science with a newspaper clipping, a small piece of news announcing that a man would undergo a test to prove his paternity. These were the first steps in genetic testing, and their dissemination allowed victims to dream of definitive evidence that would serve in court: "Is there anything biological?"

And when the trials came to prove abductions and identities, it was necessary to be on the right side of history. Spontaneously, King herself reiterated to me the importance of “good scientific journalism” in those days: “What the scientific press did was explain clearly and directly what genetic testing could provide as evidence for or against a relationship. The clarity of that disclosure prevented the military from convincing the judges of their claim that we practiced voodoo.” Voodoo? “That's what they called genetic testing when we brought the first cases to court,” King recalled.

“I am a geneticist, and throughout my career, I have had the privilege of addressing very important questions,” the scientist said in Argentina in 2023, during a visit to the Grandmothers and their recovered grandchildren , whom she has always continued to support. “The most important questions come from the people,” she asserted. Hers is the best example that science can and should be a tool for “the good” and for “the people.”