In the first decades of the 20th century, scientists around the world proposed a fantastic array of new methods to determine a child’s biological parentage. In Austria, a physical anthropologist developed a paternity test based on a comparison of dozens of physical traits—eye color, nose shape, the form of the head—between child and putative parent. In Brazil, a dentist claimed he could reveal the secret of paternity by examining teeth. And in San Francisco, physician Albert Abrams introduced the oscillophore, a miraculous machine that established parentage by measuring the electronic vibrations of the blood.  

The scientific pursuit of family identity was a product of its moment. The 1920s and 1930s were the heyday of hereditarianism, the belief that heredity decisively shaped human nature and difference. It was the era when eugenics shaped policies towards marriage and immigration, and race science was a legitimate field of inquiry. In the era of DNA, it’s tempting to lampoon this prehistory of genetics. An electronic paternity test? Who were these “scientists” who made such ludicrous claims? How could courts and the public have been so gullible?

The quest for a scientific method to determine a child’s paternity harnessed ideas about heredity to solve a practical problem: how could you tell if two individuals were related? It was a question that cropped up in a wide variety of contexts, and courts, for one, were eager for the answers provided by science. In Vienna, where illegitimate births were common, courts had become clogged with a backlog of child support cases. It was a local judge flummoxed by the messy he said/she said conflicts who first approached the anthropologist about developing a “science of resemblances.” In São Paulo, the dentist’s paternity test was applied in inheritance disputes. In one case, a railroad worker claiming to be the son of a wealthy, recently deceased Portuguese immigrant presented the dentist’s analysis. Declaring the scientific evidence a “sensational revelation,” the court declared him the man’s son.

Ordinary people were likewise captivated by the new scientific methods. After Abrams’ oscillophore made the newspapers, he received inquiries from far and wide. One was from a woman in a small town in Oklahoma, who wrote in 1921 when her estranged husband refused to recognize their newborn daughter. “I see by the papers that you can test blood and wondered if you would help me any in my case,” she wrote. “I am so sorry to think a father would do such a thing and I want to show to the world and also to him and his lawyers [and] also mine that it is realy [sic] and truly his.”

The oscillophore may not have worked in the conventional sense of the word, but it certainly did in another sense: it promised definitive answers to pressing social questions that in the early 20th century animated courts, individuals and societies.

Enigmas of identity were, of course, nothing new. From Shakespeare to the Victorian novelists, literary fathers brooded over the paternity of their children, and literary orphans wondered about their parents. But for many observers, the modern world had intensified dilemmas of identity and inspired new anxieties about sexuality and family. Science entered conflicts between estranged lovers and spouses at the very moment when women’s newfound social, sexual and political freedoms prompted critiques of the “tyranny” of modern women. It was probably not by chance that the oscillophore, which promised to reveal the adulterous secrets of wives, debuted just months after the 19th Amendment gave American women the right to vote.

Elsewhere genetic testing addressed other momentous changes. In communities transformed by mass migration and urban growth, science replaced older ways of knowing identity. Once upon a time, inheritance disputes—was this man the father of that child?—revolved around the testimony of neighbors and other community members who could attest to their relationship. But in a city of strangers, who could know for certain who was whose father? In major cities, scientific methods entered inheritance cases when older ways of knowing no longer seemed reliable.

In yet another scenario, it was the identity of mothers, not fathers, that was thrown into doubt. In the 1920s, American women began giving birth in hospitals. But the modern maternity ward gave rise to a new problem: the possibility of baby mix-ups. A series of sensational cases of alleged baby swaps occurred in Atlanta, Cleveland and Chicago over the course of the decade. Once again, scientists were called upon to resolve a quandary that would have been unthinkable when babies were born at home.

New scenarios demanding the insights of parentage science continued to crop up as the 20th century marched on. In the wake of the two world wars, French, Italian and German families appealed to scientists to reunite families that had been separated by conflict. Still later, in the Cold War, government officials drew on scientific tests to verify the identities of migrants seeking to reunite with their kin. Changing gender roles and sexual mores, urbanization, demographic growth, war and immigration: to many observers, the vicissitudes of modern life had unmoored the intimate ties of kith and kin. To these predicaments, modern science promised a miraculous antidote.

The 1980s marked a watershed in the history of genetic testing, when a British scientist developed the powerful technique known as DNA fingerprinting. By scientific and popular consensus, DNA works. Yet the work that it does is not so different from the old tests of teeth, ears, and blood vibrations. Today as in the past, paternity tests are marketed to doubting men seeking “peace of mind.”

Ineffable questions of identity are still with us, and indeed the commercial testing industry has transformed genealogical discovery into a hobby. Meanwhile, the science of parentage has become thoroughly institutionalized in state practices ranging from child-support proceedings to immigration cases.

In the present as in the past, genetic science is called on to answer a remarkable array of questions. It promises to defend morality, ensure justice, secure the nation, reknit ties and reveal the elusive truth of identity. The science may be radically different, but in the era of DNA, as in the era of electronic paternity tests, perhaps the most powerful and enduring truths genetic testing reveals are not about biology but about society.