WASHINGTON – When on March 26 the Supreme Court hears oral arguments about whether California’s ban on same-sex marriages violates the constitutional right to “equal protection of the laws,” these arguments will invoke the intersection of law and social science. The court should tread cautiously, if at all, on this dark and bloody ground.

The Obama administration says California’s law expresses “prejudice” that is “impermissible.” But same-sex marriage is a matter about which intelligent people reasonably disagree, partly because so little is known about its consequences.

When a federal judge asked the lawyer defending California’s ban what harm same-sex marriage would do to the state’s interests in “the procreation purpose” of heterosexual marriage, the lawyer said, “I don’t know.” This was mistakenly portrayed as a damaging admission. Both sides should acknowledge that, so far, no one can know.

A brief submitted to the U.S. Supreme Court concerning the California case by conservative professors Leon Kass and Harvey Mansfield and the Institute for Marriage and Public Policy warns that “the social and behavioral sciences have a long history of being shaped and driven by politics and ideology.” And research about, for example, the stability of same-sex marriages or child rearing by same-sex couples is “radically inconclusive” because these are recent phenomena and they provide a small sample from which to conclude that these innovations will be benign.

Unlike the physical sciences, the social sciences can rarely settle questions using “controlled and replicable experiments.” Today “there neither are nor could possibly be any scientifically valid studies from which to predict the effects of a family structure that is so new and so rare.” Hence there can be no “scientific basis for constitutionalizing same-sex marriage.”

The brief does not argue against same-sex marriage as social policy, other than by counseling caution about altering foundational social institutions when guidance from social science is as yet impossible. The brief is a pre-emptive refutation of inappropriate invocations of spurious social science by supporters of same-sex marriage.

For example, a district court cited Dr. Michael Lamb, a specialist in child development, asserting that the “gender of a child’s parent is not a factor in a child’s adjustment” and that “having both a male and female parent does not increase the likelihood that a child will be well-adjusted.” The conservatives’ brief notes that, testifying in the trial court, Lamb “had conceded that his own published research concluded that growing up without fathers had significant negative effects on boys” and that considerable research indicates “that traditional opposite-sex biological parents appear in general to produce better outcomes for their children than other family structures do.”

The brief is replete with examples of misleading argumentation using data not drawn from studies satisfying “the scientific standard of comparing large random samples with appropriate control samples.” The late Sen. Daniel Patrick Moynihan, a distinguished social scientist, said the “pronounced” liberal orientation of the social sciences is “well established” and explainable: “Social scientists are frequently caught up in the politics which their work necessarily involves” because social science “attracts persons whose interests are in shaping the future.”

This helps explain why “Brandeis briefs” have shaped American law. Before joining the Supreme Court, Louis Brandeis defended constitutional challenges to progressive legislation by using briefs stressing social science data, or what purported to be such, rather than legal arguments. He advanced his political agenda by bald assertions inexcusable even given the limited scientific knowledge of the time. For example, in his 1908 defense of an Oregon law restricting the number of hours women could work, he said “there is more water” in women’s than in men’s blood and women’s knees are constructed differently.

Since Moynihan wrote the above in 1979, the politicization of the social sciences has become even more pronounced, particularly in matters of “lifestyle liberalism.” Hence the need for judicial wariness about social science that purports to prove propositions – e.g., that same-sex marriage is, or is not, harmful to children or society – for which there cannot yet be decisive evidence.

If California’s law is judged by legal reasoning, rather than by social science ostensibly proving that the state has no compelling interest served by banning same-sex marriage, the law may still be overturned on equal protection grounds. But such a victory for gay rights, grounded on constitutional values, and hence cast in the vocabulary of natural rights philosophy, would at least be more stable than one resting uneasily on the shiftable sand of premature social science conclusions.

© 2013, Washington Post Writers Group