Camille Robcis is an associate professor of history and French at Columbia University and author of “The Law of Kinship: Anthropology, Psychoanalysis, and the Family in France.”

Since 1994, France has banned surrogacy and restricted access to reproductive technologies to heterosexual couples who have been married or living together for more than two years, forcing single women and lesbian couples to travel to neighboring countries for fertility treatments, and gay men to resort to surrogates in countries such as the United States or the United Kingdom. On Tuesday, the French National Assembly is scheduled to vote on a bill that would finally allow access to assisted reproductive technologies, including IVF, for unmarried women and lesbian couples. Under the proposed law, the treatments would be reimbursed by Social Security, and French doctors helping these women with fertility treatments would no longer face legal sanctions. Surrogacy, however, would remain illegal.

Outside of France, the bill — and the reaction to it from the French public — has been met with bemusement. Many observers have expressed surprise that IVF access in France was restricted in the first place — and even more surprise at the furious polemic that has been unleashed in response.

After a month of fierce legislative debates that have resulted in more than 2,000 proposed amendments to the bill, an estimated 75,000 marchers took to the streets of Paris on Oct. 6 in opposition. Some of the protesters dressed up as Marianne, the symbol of the French Republic, with red Phrygians caps and blue-white-red banners. Some waved flags calling for “Liberty, equality, paternity,” a reference to the revolutionary slogan “liberté, égalité, fraternité,” while others carried posters with the motto “Marchons Enfants,” an allusion to the first words of the French national anthem.

The fact that the protesters drew upon these traditional symbols of the nation is not incidental. They see this debate, like the law to legalize gay marriage in 2013, as a challenge to their very vision of French citizenship and belonging. At stake is not simply the extension of reproductive rights to a larger segment of the population, but also a debate that will frame the limits of what a future French family and citizenry will look like. And, indeed, France’s legal and social structure has long been entwined with the heteronormative order and idea of a traditional family.

The foundational text of French family law, the 1804 Napoleonic Civil Code, presented the family as a “small homeland,” a vector of integration into the collective social body. As Napoleon and his legal advisers saw it, the French Revolution and especially the Terror had done away with familial stability by legalizing divorce and recognizing natural children. In reaction to this, the code consecrated the heterosexual family as the structure organizing French society.

This trend continued for centuries and is still evident today. It played a significant role in the 1939 Family Code that regulated family policy and was incorporated in Social Security after World War II. The generous policy of family benefits that France is still well-known for was welcomed across the political spectrum because it presented the family as central to the postwar social contract and French welfare state. To this day, the governmental ministry in charge of family affairs has also been in charge of solidarity, social cohesion and integration.

This context helps explains why the IVF bill and push for marriage equality elicited such strong responses: Both movements challenge this vision of the heterosexual family as constitutive of the nation. The current bill is in many ways designed to remedy the gaps in the 2013 “Marriage for All” law that legalized marriage and adoption for same-sex couples. The law also unleashed a furious debate that played out in the legislature, courts, the media and the streets, with some protests reaching 300,000 participants. Politicians were harassed, scholars and journalists were heckled, and LGBT people were attacked in public spaces. The week of the vote, the president of the National Assembly received an envelope filled with gunpowder that threatened war unless he suspended voting.

Even then, the opposition centered on what marriage equality would mean for reproductive rights. Taken aback by the backlash against his bill, then-President François Hollande chose to shelve the question of reproductive technologies. Now, as the government pushes forward on measures to resolve these questions, those same forces have risen up once again.

Like the debates over race and immigration that have played out in France in recent years, the struggle over IVF and reproductive rights touches on one of the fault lines of the French Republic. Underlying these disputes is the question of whether French law — and the republic more generally — should function as an abstract ideal frozen in time, or whether it should adapt to reflect the diversity of race, gender and sexuality that exists in the country today. This bill, at least, is a step in the right direction.

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