SAN FRANCISCO — Attorneys working to eradicate California’s Proposition 8 played up the adverse effects it’s had on same-sex couples during the first week of the landmark federal trial.

Attorney Ted Olson, who’s helping represent plaintiffs seeking to strike down the law that bars same-sex couples from marrying, encapsulated the case during his opening arguments.

“There is no rational justification for this unique pattern of discrimination,” he said. “Proposition 8, and the irrational pattern of California’s regulation of marriage, which it promulgates, advances no legitimate state interest. All it does is label gay and lesbian persons as different, inferior, unequal, and disfavored. And it brands their relationships as not the same, and less-approved than those enjoyed by opposite-sex couples.

“It stigmatizes gays and lesbians, classifies them as outcasts, and causes needless pain, isolation and humiliation.”

Among the first witnesses called during the trial, which is expected to run several weeks, were experts who’ve studied the societal effects of same-sex marriages. Harvard University professor Nancy Cott at one point was asked what effects such unions have had on divorce rates.

“My only comment is from observing my own state of Massachusetts, where there has been same-sex marriage for five years,” she said. “Massachusetts has [the] lowest divorce rate in country. Since five years ago, [the] divorce rate has fluctuated slightly, but if anything, [it] is lower.”

Speaking outside of court, plaintiff questioner Theodore Boutrous Jr. lauded Cott as an “expert on the history of marriage in the United States” who helped propel the plaintiffs’ case forward during the trial’s first week.

Boutrous said Cott made it clear “that the history of marriage in the United States can be characterized by the fact that this nation has time and again knocked down and eliminated barriers to marriage that were discriminatory and unfair.”

“It was very powerful to hear her talk about the history of discrimination, beginning with slavery and when the slaves were freed,” he said. “One of the first things that happened was an explosion of people who had been slaves wanting to get married because of this badge of citizenship and freedom.

“And other restrictions on women, on Asians on other groups who were targeted in our past — those restrictions were struck down as our society recognized those were unfair. That is a powerful testament to liberty and due process and equal protection in this country.”