Prof. Nancy Cott is currently testifying in Perry vs. Schwarzenegger, the "Prop 8 Trial."
She's an expert on the history of marriage in the US.
Here's the blurb from NPR's Fresh Air page, from 2004.
"Cott is a professor of history at Harvard University. She testified before Vermont's judiciary committee. Vermont became the first state in the country to make civil unions legal for gay and lesbian couples. Cott is the author of Public Vows: A History of Marriage and the Nation (Harvard University)."