A federal court turned to historians Tuesday as it considers the constitutionality of Proposition 8, an amendment that banned same-sex marriage in California.

Harvard professor Nancy Cott told a federal court in San Francisco that child rearing was only one of several purposes of marriage, not "the central or defining purpose," the Los Angeles Times reports.

She noted that that divorce rates rose steeply in the 1960s and marriage continued to be viewed negatively in the 1970s as heterosexuals advocated "open marriages" and "swinging." But divorce rates hit a plateau in the 1980s, and marriage is now held in high esteem in the U.S., she said.

She attributed the higher status of marriage to advocacy by the Christian right and the growing clamoring of gays and lesbians to participate in it.

During cross-examination, lawyers for the Proposition 8 campaign noted that racial restrictions on marriage in the U.S. were never as "uniform" or widespread as the ban on same-sex marriage. He also asked Cott if it was possible to predict the consequences same-sex marriage would have on society.