The enormous turquoise van noses through midtown traffic and parks on commercial avenues or in leafy neighborhoods, attracting the curious glances of passersby. On its side is emblazoned an unlikely slogan: “Who’s Your Daddy?” The vehicle is a mobile DNA unit, owned by the company Health Street. Since 2012 its founder and CEO, Jared Rosenthal, has hawked paternity tests to New Yorkers like soft-serve ice cream. “No one really knows who they are,” Rosenthal said in a New York Times profile, remarking that people have been asking questions about paternity for as long as couples have been making babies. “Only now we have a test.”

The pervasive and routine question of paternal identity reflects fatherhood’s profound economic, political, and cultural stakes.

It is telling that fatherhood, not motherhood, is posed as a question, the monetizable secret to knowing who we are. Indeed for much of history paternity has been thought of as naturally uncertain, as opposed to the obvious and unproblematic fact of maternity. To some extent we are still beholden to these ideas; many would find the question “Who’s Your Mommy?” absurd, even as new reproductive technologies (surrogacy and IVF) and family forms (same-sex couples and polyamorous arrangements) complicate the old idea of maternal certainty. In patriarchal societies, the most important resources—economic support, patrimony, nationality (in short, an “identity”)—are still transmitted by fathers. The pervasive and routine question of paternal identity reflects fatherhood’s profound economic, political, and cultural stakes. Over the last hundred years, it has inspired attempts to find ever more definitive answers.

The Who’s Your Daddy truck epitomizes this quest. The groundbreaking development of DNA technologies, coupled with the explosive rise of a global commercial market for paternity testing, has marked a brave new era in the millennial search for the father. More powerful technologies are accessible to more people around the world than ever before. States as well as consumers have driven expanded applications of paternity science; potent political discourses reinforce the right to paternal knowledge; and courts appeal to paternity testing to resolve an array of criminal and civil disputes, from citizenship to child support.

The quest for the father—deeply politicized, culturally fetishized, and now thoroughly commercialized—did not end with the advent of DNA.

For all their novelty, however, these developments recapitulate rather than revolutionize the history of paternity in the twentieth century. The idea Rosenthal sells—that paternity is a biological relationship, that it can and should be known, and that science is the way to know it—is a relatively recent development. It makes assumptions—about what paternity is, why we need to know it, and how it can be known—that are by no means universal. These ideas became increasingly powerful in the first decades of the twentieth century, not only in the United States but across the Americas, north and south, as well as in Europe. Tentatively at first, and then with increasing enthusiasm, these beliefs and techniques found practical application from Buenos Aires to Berlin to Los Angeles. As they did, they spawned boundless fascination among transatlantic publics and shaped the way states and societies thought about kinship, identity, and belonging.

But like any new technology, paternity science has raised a host of practical and ethical questions. In what circumstances should tests of parentage be performed? Who should have access to the results? And is knowing always a good thing? If fatherhood was traditionally determined by the community, the judge, the mother, and the man himself, modern paternity science has vested enormous power in a new authority, the biomedical expert. What happens when the technician’s results collide with alternative social and legal notions of paternity? Despite promising a golden age of certainty, the dramatic advances of the DNA era have failed to resolve our longstanding cultural and legal uncertainty about what paternity is in the first place. The father is as ambiguous, as deeply contested, indeed as elusive, as ever.

This story begins at the end of the twentieth century, when the science of paternity saw remarkable scientific advances, culminating in DNA fingerprinting. Pioneered in the early 1980s by British geneticist Alec Jeffreys, the technique is perhaps most closely associated with forensic identification in criminal cases—it is in that context that O. J. Simpson’s attorneys Barry Scheck and Peter Neufeld, who would go on to found the Innocence Project, referred to it as the “gold standard for truth telling”—but its earliest application was to demonstrate not individual identity but parentage. Every individual’s sequence of base pairs is unique, but because they are inherited, the DNA from two people can be compared to determine the probability that they are related. For the first time in human history, it became possible to establish paternity with a 99.99 percent degree of certainty.

For the first time in human history, it became possible to establish paternity with a 99.99 percent degree of certainty.

Scientific discovery soon catalyzed commercialization, and with it the “truth machine,” as former Attorney General John Ashcroft put it, became faster, cheaper, and more accessible. Today, some genetic testing companies promise a turnaround of just days and charge as little as $79 a test. The chief U.S. lab accreditation agency reports that the number of paternity tests under its auspices increased by almost 400 percent between 1988 and 2010, up to around 400,000 a year—and that figure represents only a fraction of the total number, because only half of all labs are accredited, only 60 percent of those that are accredited report their data, and these figures do not include do-it-yourself tests. One industry expert estimates the true number at over one million tests annually, and projects that genetic testing will be a $3.8 billion dollar industry by 2023. In the age of DNA, modern paternity has become thoroughly commercialized thanks to a profit-seeking behemoth, Big Paternity.

Indeed Big Paternity has gone global, expanding well beyond its transatlantic cradle. British and U.S. companies specializing in paternity and relationship testing now operate on six continents. Because testing does not require proximity to a lab—customers can purchase kits online and mail in their samples—it can be marketed anywhere there is Internet access and mail service. California-based EasyDNA offers testing in thirty-nine countries, from Uganda to Ukraine. The website for United Kingdom–based Nimble Diagnostics explains paternity testing procedures in thirty-six languages. Chinese and Indian biotech companies have also capitalized on the new opportunities. The owner of a private lab in Beijing reports a 20 percent increase in paternity testing requests since 2000, and Delhi-based Indian Biosciences (offering “indisputable answers to emotional questions”) operates collection centers in 150 cities across India.

Big Paternity has gone global, expanding well beyond its transatlantic cradle.

As in the past, states are avid consumers of these technologies. A significant portion of genetic testing continues to take place under the aegis of courts and other state agencies, for child support, custody, or immigration cases. In the United States, “legal forensic services” outsourced to private labs account for about 45 percent of the market.

Scientific advances make new applications possible, but it is social and political exigencies that make them necessary. The explosion of state-sponsored paternity testing in the United States dates from the 1970s—a decade before DNA fingerprinting became possible—and coincides with the rollback of welfare and rising rates of extramarital birth. Beginning with the Social Security Act of the 1930s, the federal government’s welfare programs created incentives for the states to find fathers. By the late 1970s, technology was powerful enough to positively identify progenitors rather than just exclude impossible ones. Meanwhile, extramarital birth rates quadrupled between 1950 and 1980, reaching unprecedented levels. Courts and legislatures proved eager to find fathers for poor children who would otherwise fall on the welfare rolls, and by the early 1980s blood testing had skyrocketed.

Paternity was increasingly a matter for the lab rather than the courtroom.

The new scientific tests presented an expedient way to resolve claims. A simple blood draw dispensed with protracted, messy, and expensive legal sagas. Paternity was increasingly a matter for the lab rather than the courtroom—so much so that some states held that because the scientific evidence was incontrovertible, indigent fathers in paternity cases had no right to counsel. The momentous 1996 reform that dismantled the U.S. welfare system further institutionalized the use of genetic testing. It required that mothers cooperate to establish fathers’ identities as a condition of aid, ordered the states to use genetic tests to do so, and invested those tests with conclusive power to fix paternity. By 2000 states were spending more than $32 million on lab tests each year.

The United States has not been alone. The enthusiastic embrace of testing among Latin American states in the last two decades reflects an even more remarkable historical watershed. In the nineteenth century, civil law—the tradition practiced in much of continental Europe, Latin America, and European colonies, as opposed to the common law tradition in Anglophone countries—defined paternity in social and volitional terms: the father was the man who publicly and willingly performed this role before the community. In this older tradition, biological paternity was considered an ineffable enigma of nature, not just unknown but indeed unknowable. Paternity was less physical than metaphysical, a relationship deduced from behaviors and social conventions. In many legal traditions, it was marriage that made paternity: the father was the husband of the mother. As for a child born outside of marriage, the father was revealed in other ways: he was the man who cohabitated with the mother or kissed the baby in public, the man whom the neighbor had seen paying the wet nurse. Paternity was not primarily a natural fact deriving from the act of procreation; it was a social fact brought into being through a man’s words and deeds and the observations of the community.

In an older tradition, paternity was defined in social and volitional terms: the father was the man who publicly and willingly performed this role before the community.

Following this social logic, mediaeval doctrine held that if a widow remarried quickly and then gave birth, the child could choose its father, depending on whether it was more advantageous to be the youngest child of the first husband or the oldest child of the second one. Other legal traditions have provided for partible paternity. Scandinavian law, for example, held that if two men had a relationship with the mother, support for her child might be split between them. It could also be partial: a man might be responsible for supporting a child economically but not give that child his name or inheritance. When paternity was disputed, those called to elucidate it were not scientists or doctors but friends, associates, the neighbors, the mother, or the man himself. Some children simply had no father. In Anglo-American law, the illegitimate child was historically deemed a filius nullius, a child of nobody. If many circumstances demanded a father, in others “who’s your daddy?” was deliberately left unanswered. In slave societies, the father of the enslaved child might well be the mother’s owner. And what about the debauched priest, or the case in which the husband was not the father of his wife’s child? Colonizers and soldiers deployed in foreign lands have often been excused from responsibility for the children they engender there. Because paternity is embedded in social relations of power, it is also potentially disruptive. Politics, morality, and the public purse might require a father in some situations but demand something else—discretion, suppression, invention—in others.

In the twentieth century, by contrast, modern paternity redefined fatherhood as a biological and obligatory relationship. Recent public policies in Latin America have capitalized on this idea, as countries across the region have pursued “responsible paternity” campaigns to systematically identify fathers and compel them to take economic responsibility for their children. The task appears especially urgent in a region where marriage rates are low, extramarital birth rates high (in several countries, in excess of 70 percent), and many poor children are reared by mothers on their own—trends that policy makers believe contribute to female and child poverty.

In the past paternity was not a natural fact deriving from the act of procreation; it was a social fact brought into being through a man’s words and deeds and the observations of the community.

“Responsible paternity” schemes draft DNA into these efforts. At least a dozen countries have passed laws making testing available to poor people paid for by the state. In Brazil, which boasts an especially ambitious campaign to find errant fathers, mobile DNA testing vans fan out to hundreds of poor, urban neighborhoods and hardscrabble provincial towns. Here is a very different sort of Who’s Your Daddy truck, one that circulates under the aegis not of a health entrepreneur but of the state, not to resolve personal questions about identity but to establish legal paternity and secure child support. The task of locating genetic fathers is imbued with vast and dubious powers to ameliorate social problems. In communities grappling with poverty, crime, police violence, and inadequate housing, health, and education, DNA testing promises a quick, apolitical techno-fix.

Such policies have attracted remarkably widespread political support. Feminists and child rights advocates regard responsible paternity as a boon to gender equality and child welfare. Conservatives tout how these measures strengthen the family and promote individual responsibility. Meanwhile, it is no coincidence that paternity science has gained ascendance in an era of downsized states and social disinvestment. In Latin America as in the United States, paternity testing is an expedient tool for privatizing responsibility for poor children. If modern paternity was in part the creation of early-twentieth-century welfare states, ironically the retrenchment of those states at the end of the century has further galvanized efforts to find the father.

Another state priority, national security, has also spurred parentage testing.

Testing kinship at borders has a long history. The Cold War–era U.S. immigration service pioneered this use of parentage testing when it began drawing the blood of Chinese migrants. Today more than twenty countries in Europe, North America, and Oceania routinely use genetic analysis to verify family relations among immigrants and refugees seeking to reunite with family members. (Apparently the only place outside of North America, Europe, and Oceania to do so is Hong Kong, which tests Chinese applicants—perhaps a legacy of the U.S. consulate’s policy in the 1950s.) Receiving countries typically require DNA evidence when applicants’ documentary proof of family relation is unavailable or considered unreliable.

Politics, morality, and the public purse might require a father in some situations but demand something else—discretion, suppression, invention—in others.

In practice, the subjects of testing are almost always nonwhite immigrants from the global south. “The genetic tie is inherently paradoxical,” notes legal scholar Dorothy E. Roberts. “It is at once a means of connection and a means of separation. It links individuals together while it preserves social boundaries.” The boundaries that paternity testing preserves in this context are simultaneously national and racial. This is not only because, as a biologist who now regrets giving his parents 23andMe kits observes, ancestry testing services are “essentially really advanced paternity tests.” It is also because of the abiding cultural logic in which ethnicity remains the sap of the family tree. In the imaginary surrounding paternal uncertainty, obsessions with racial ambiguity, mixing, and substitution continue to flourish.

Such boundary making is not uncontested. In 2006, France passed a controversial law expanding the uses of DNA testing in family reunification, a policy that implicitly targeted African immigrants. Echoing the Chinese American community of the 1950s, antiracism advocates denounced testing as “detestable,” and the policy was scrapped a few years later.

The creeping use of DNA testing in the United States, in contrast, has received less public scrutiny. The application of DNA testing to “national security” expanded exponentially after September 11, 2001. In 2008, officials suspended a program to reunite Somali refugees with family members residing in the United States after a pilot DNA program revealed that many refugees were not biologically related to their sponsors. In an argument that could have been lifted directly from the Immigration and Naturalization Service inspectors of the 1950s, a government memo warned that “leaving open loopholes that allow potential terrorists, or simply fraudulent applicants to insert themselves in legitimate family groups not only threatens our security” but wastes “vast resources.” When the Somali program was reinstated four years later, it featured a beefed-up DNA requirement. Just last month, the Department of Homeland Security began using portable “rapid DNA” machines to test family relations among Central American migrants at the U.S.-Mexico border. This state-of-the-art technology, which can establish biological kinship from cheek swabs in about ninety minutes, may soon became a standard feature of the world’s borders, immigration offices, and refugee camps. For its part, the biotech industry forecasts an annual growth rate of “DNA analysis in Homeland Security” of close to 14 percent, as well as opportunities for expansion in Asia and Europe.

If many contemporary state uses of parentage testing have precedents in the past, some appear genuinely novel. In Argentina genetic technologies have been mobilized to address human rights violations committed during the country’s Cold War military dictatorship. In a now notorious episode, authorities kidnapped some 500 children from parents considered to be political dissidents and placed them in irregular adoptions. Decades later, the Abuelas, an organization of the children’s grandmothers, led the charge to locate the kidnapped children and restore their natal identities. As a result of their efforts, in 1987 Argentina established a national genetic database to assist with reunifications.

Seventy years later, another genetic innovation was born here: the índice de abuelidad, or “index of grandpaternity,” a technique used to establish the genetic link between two people separated by a generation. (The Abuelas joked that the fact the technique used mitochondrial DNA, inherited through the mother, was proof that god was female.) It is yet another example of how politics—in this case, the quest for justice in the aftermath of state terror—fuels genetic innovation. And the politically motivated removal of children from their parents is hardly an Argentine peculiarity, of course. In Spain, dictator Francisco Franco kidnapped some 30,000 children from their dissident parents. For several weeks in the spring of 2018, the Trump administration systematically seized thousands of Central American migrant children at the U.S.–Mexico border. In the wake of these episodes of state-sponsored abduction, DNA has been used to facilitate reunifications.

The expanding demand for kinship science is fueled not just by state policies or abuses but also by private demand. The enduring popular fascination with origins has long spurred such technologies; Big Paternity has commercialized that allure. Today the curious, the uncertain, and the aggrieved can purchase what the industry calls “discretionary” or, more colorfully, “peace of mind” tests for their own personal reasons.

Within a decade of the emergence of DNA fingerprinting, for example, the company Identigene began marketing paternity tests directly to U.S. consumers and four years later sold the first test on the Internet. By 2007 test kits became available in pharmacies. Easy, accessible, and increasingly inexpensive, home testing today accounts for more than 36 percent of the U.S. DNA market and is also available to consumers from Australia to South Africa, Italy to Malaysia.

In France, the child’s right to a father—even a nonbiological one—trumps the parent’s or child’s right to genetic knowledge.

Commercialization has in turn reshaped who has access to the truths paternity science tells. Modern paternity sought to transplant paternal truth from the courtroom to the laboratory. Now Big Paternity has uprooted it from both, propagating it on the Internet, on the pharmacy aisle, and in the mobile van. Modern paternity has promoted the categorical advantages of knowing the father, but in practice that prerogative has always been tempered by concerns about the destabilizing effects of unchecked knowledge. Even its avatars warned of such dangers, as when doctors and lawyers in Catholic countries insisted that protecting marriage, public propriety, and the child’s legitimacy trumped any inalienable right to biogenetic truth. Paternity science had to be applied in judicious, socially responsible ways, with the courts and scientists themselves as the gatekeepers.

Some observers express deep reservations about the prospect of consumers testing without the explicit consent and participation of all parties, particularly when the well-being of minors is at stake. In France—where doctors once warned that including ABO blood types on identity cards might unwittingly expose adulterous children—private parentage testing is today illegal: tests can be obtained only with a court order. (Article 16-10 of the Civil Code, adopted in August 2004, says, “An examination of the genetic particulars of a person may be undertaken only for medical purposes or in the interest of scientific research.”) The state asserts the prerogative to protect the parent-child relationship and to manage potentially harmful information about kinship. The child’s right to a father—even a nonbiological one—trumps the parent’s or child’s right to genetic knowledge.

But to many today, such policies appear quaint, paternalistic, and, in any event, futile. Evasion of the French law appears to be widespread. Labs in Spain and Switzerland report a booming business testing surreptitious tissue samples sent by French citizens, who risk steep fines and even jail time for skirting the law. In any event, France’s restriction of paternity testing is striking mostly because it is exceptional. Elsewhere, private testing tends to be regulated loosely, if at all. Some countries prohibit testing without the consent of both parents, but in practice it is often possible to submit a toothbrush or hair sample without the knowledge of its owner. Almost as if they were speaking directly to the circumspection of earlier testers, industry analysts boast that what is “revolutionary” about paternity testing today is that it does “not require involvement of doctors or lawyers.” Genetic knowledge has become a de facto prerogative, conferred not by deliberate legislation but by the vast commercial reach of the testing industry itself. Big Paternity has achieved what modern paternity did not.

If the erasure of natal identity in the twentieth century has often resulted from political forces, then so too must its recuperation.

Access to genetic knowledge is the product of political developments as well as commercial ones. The past half century has witnessed an increasingly powerful discourse surrounding the individual’s right to know his or her origins, defined implicitly or explicitly in biogenetic terms. This right is codified in international child rights treaties, most notably the 1989 United Nations Convention on the Rights of the Child, which holds that “children have the right to an identity.” (Argentina’s Abuelas lobbied to have this article included.) This has become a rallying cry of adoptee rights organizations such as Bastard Nation, a North American group that lobbies to open sealed records containing adoptees’ “historical, genetic and legal identities.”

Advocates assert that donor-conceived people have such a right in the context of assisted reproductive technologies. In the “responsible paternity” campaigns in Latin America, the right to a father is often framed in terms of the child’s right to an identity. If the erasure of natal identity in the twentieth century has often resulted from political forces—state violence, repressive social norms, patriarchal prerogatives, racism, war—then so too must its recuperation.

One conclusion to be drawn from this history is that distinct ways of defining paternity have no necessary politics. Biological essentialism is not inherently “conservative.” Genetic kinship can be mobilized as part of a state’s murderous racial ideology, in the name of welfare privatization, or for national security, and it can be a rallying cry of men’s rights groups that wear misogyny on their sleeve. But it can also be championed by human rights activists such as the Abuelas of Argentina and by advocates of adoptee and children’s rights. As sociologist Alondra Nelson has shown, genetic evidence is also central to “reconciliation projects,” legal and political efforts in which black Americans seek to establish connections to African origins, restore lost personal and collective histories, and press for reparations.

Distinct ways of defining paternity have no necessary politics. Biological essentialism is not inherently “conservative.”

Nor is there anything inherently “progressive” about a social constructivist vision of kinship. Napoleonic tradition defined paternity in terms of male volition, social performance, and contract—a socio-affective definition if there ever was one. But it did so to the benefit of patriarchal privilege, privacy, and property and at the expense of unmarried women and their children. In 1998, as Chilean lawmakers prepared to pass a reform allowing mothers and children to bring suits to establish the identity of illegitimate fathers for the first time since the nineteenth century, some conservatives expressed opposition. Should a child with no relationship to its progenitor be allowed to show up one day, make financial and moral claims on him, and disrupt his legitimate family, merely because of a genetic link? They argued that allowing such actions privileged a narrowly biological paternity over a more socially meaningful one based on affection, responsibility, and paternal will. And in the U.S. Supreme Court case Michael H. v. Gerald D. (1989), even conservative justice Anton Scalia marshaled a social constructivist kinship when he assigned paternity to the husband and not the biological father of the child in question.

A global perspective reveals paternity’s political contingency with special clarity. The “truth machine” of DNA has become a routine part of judicial practice, public policy, media culture, and social life across an ever greater swathe of the planet. There is an unprecedented consensus among scientists, legal experts, and the public that the technology “works.” But as in the past, the work it does continues to be dramatically shaped by local circumstance. In Latin America many feminists have embraced DNA testing to combat irresponsible paternity, which they characterize as “a form of economic and emotional violence against women.” In India women’s rights advocates have emphatically opposed its growing use as a cynical weapon used to control wives. Paternity may be inherently political, but it has no preordained politics. Context is everything.

The truly significant question about paternity is not empirical—Who is the father?—but normative: What do we want him to be?

Many observers over the course of the twentieth century predicted that the perfection of paternity science would herald a watershed in the millennial search for the father. “With a scientifically accurate determination of paternity,” a Baltimore newspaper prophesied in 1922, “a world of misery, suspicion, lies and faithlessness would be abolished from the earth.” In Childhood’s End (1953), science fiction writer Arthur C. Clarke predicted such a technology would bring about the end of marriage. In the 1960s, a Scottish jurist mused that it would be as explosive as nuclear physics. At the dawn of the DNA era, an American geneticist speculated that while motherhood had always been certain, now fatherhood would be as well: “We will have come one step closer to equality of the sexes.”

Not one of these spectacular predictions has come to pass. The quest for the father—deeply politicized, culturally fetishized, and now thoroughly commercialized—did not end with the advent of DNA. On the contrary, at the very moment that science has promised paternal certainty for the first time in human history, uncertainty as a cultural force appears as powerful as ever. This is in part because a global industry commercialized doubt. It is in part because, as recreational testing shows, DNA can just as easily create mysteries as solve them. But above all it is because science was never capable of finding the father in the first place. It was not a lack of knowledge that produced the quest for the father; the quest was always a social and political one. The truly significant question about paternity is thus not empirical—Who is the father?—but normative: What do we want him to be?

Editors’ Note: This essay is adapted from the author’s new book Paternity: The Elusive Quest for the Father, published by Harvard University Press.