Next Tuesday, April 28, oral arguments begin in Obergefell v. Hodges, a Supreme Court case which may decide the fate of same-sex marriage in the United States.  Apart from hearing the parties in the cases (four are actually being considered), the nine justices on the Court can also consider briefs written by “friends of the court”, or amici curiae. More than a hundred of these have been filed, from supporters and opponents ranging from the American Psychological Association to “Mike Huckabee Policy Solutions”. Below are a few paragraphs from an amicus curiae brief written by two “scholars of fertility and marriage”, Walter Schumm, Professor of Family Studies at Kansas State University (a frequent contributor to MercatorNet) and Jason S. Carroll, Professor of Family Life at Brigham Young University. The questions have been added by MercatorNet. Why should governments care whether same-sex marriage is legal? [One reason is that] States have a legitimate interest in ensuring the orderly reproduction of society over time. This interest necessarily entails ensuring a sufficient and sustainable fertility rate. Because only opposite-sex couples can procreate, and therefore sustain a fertility rate, encouraging, promoting, and supporting the formation of opposite-sex relationships furthers the state’s interests in perpetuating the long-term survival of its citizenry and sustaining intergenerational welfare programs such as Social Security. Is same-sex marriage a contributor to fertility decline? Though there have been a number of explanations for the worldwide decline in fertility rates, and the entire explanation may be a combination of different factors, the adoption of same-sex marriage is likely to contribute to such a decline in any state, given the demonstrated effect that the adoption of same-sex marriage policies has on fertility rates.
Redefining marriage in genderless terms breaks the critical conceptual link between marriage and procreation by implicitly endorsing an adult-centric model of marriage, and diluting the implicit encouragement the institution of marriage provides for procreation by married couples. It ignores the inherently generative nature of heterosexual marriages, and sends a powerful message that procreation is not a valued societal priority. Can you prove that there is a link between same-sex marriage and declining fertility? To the extent a genderless marriage definition deemphasizes and deprioritizes procreation, it would almost certainly reduce fertility rates. While there is a notable absence of scholarly investigation focusing directly on the correlation between same-sex marriage and fertility rates in the United States, some helpful related data is available. Is there any American data about declining fertility? National Vital Statistics Reports show a noteworthy correlation between same-sex marriage and decreasing fertility rates. As of 2010, five of the seven States (including Washington DC) with the lowest fertility rates all permitted same-sex marriage (or civil union equivalents). In contrast, none of the nine States with the highest fertility rates allowed it before 2010. And while the fertility rates in both groups of States decreased between 2005 and 2010, the percentage decline was almost twice as large in the states that allowed same-sex marriage or its equivalent. How about declining marriage rates? Every state that has adopted same-sex marriage and kept the relevant data has seen a substantial decline in the rate of opposite-sex marriages over time—ranging from 5.1 percent to nearly 9 percent. Using the lower end of that range, a 5 percent reduction in long-run marriage rates in the United States, and assuming only half of that reduction would be due to marriage forgone rather than marriage delayed, that data demonstrates that additional 1.275 million women would likely forego marriage over the next fertility cycle (30 years). Under conservative assumptions and over the next 30 years, this would lead to nearly two million fewer births over just one fertility cycle. But are fewer children really that important for the US? A reduction so significant in the number of births would have a profound, continuing impact on fertility rates in the United States. At a minimum, these data strongly suggest that abandoning a heterosexual marriage definition would create or increase the risk of such a decline. Even such a clear risk amply justifies any state’s decision to retain an opposite-sex definition of marriage. But what about studies showing that there is no impact on traditional marriage? Much has been made of a 2009 study by Laura Langbein and Mark Yost, claiming to prove beyond a doubt that there is virtually no adverse impact on societal outcomes specifically related to "traditional family values," and thus no economic rationale for government to regulate or ban those choices. 
However, as Professor Walter Schumm points out,  the Langbein and Yost study had serious limitations. Those limitations are shared by later, similar analyses of state data, such as the oft-cited “Dillender study,” which argued that there is no evidence same-sex marriage reduces the opposite-sex marriage rate.  Remarkably, neither of these studies took into account the number of years since same-sex marriage had become legal in a state, nor did they examine fertility rates. They seem to share the fallacious assumption that the impact of redefining marriage would show up in measurable and statistically meaningful ways immediately after a redefinition.
As Justice Alito’s remarks in Windsor suggest, that assumption is unrealistic in the context of an ancient and complex social institution like marriage. Experts on marriage have frequently and correctly noted that such major social changes operate with a “cultural lag” that often requires several years -- sometimes a generation or two -- to be fully realized.