George Chauncey, professor of history at Yale University, and Nancy Cott, professor of history at Harvard, have been expert witnesses this week in the California trial testing the constitutionality of California's referendum-based ban on same-sex marriage. Background on the case: Margaret Talbot's New Yorker story, "A Risky Proposal," which explores how the case came to be launched by George Bush's former Solicitor General against the advice of most of the leading gay-rights advocacy organizations.
It's never easy being a historian witness in a big public policy trial, as UofT's Michael Marrus has said many times about holocaust-denial trials. Good luck to Professor Chauncey and Cott, who are tasked with demonstrating that the rationales given for excluding gay couples from marriage are groundless given (in Chauncey's case) the history of anti-gay prejudice and (in Cott's) the historical evolution of the nature of marriage in American society.
To my knowledge, no historians were involved in Barbeau v. British Columbia, one of the key legal cases that established same-sex marriage in Canada, but if you are up for reading a legal judgment (very readable, if you can get through the judicial framing), the historical evolution of marriage is very lucidly outlined in Madame Justice Jo-Ann Prowse's reasons for judgment. American courts rarely consider foreign jurisprudence, but they could benefit.