This observation from The League of Ordinary Gentlemen about the expert witnesses in Perry:

in the findings of fact Judge Walker ended up relying almost exclusively on the plaintiffs’ witnesses, above all Nancy Cott, whose work is indeed excellent. Gays and lesbians should thank her, George Chauncey, Hendrik Hartog, and indeed the entire American historical profession that supported their work. Historians have made very clear what marriage has and has not been throughout American history, even if it doesn’t necessarily square with many of our received understandings about the way things always were. The truth is that marriage has been a continuously changing institution, not one settled for all time, and that same-sex marriage is simply one more change in a direction that aligns marriage more closely with our ideals and values. Historians have performed an invaluable service to the cause of liberty and human dignity in this case.