Plaintiffs lawyers in the gay marriage trial taking place in San Francisco wrapped up their case Friday. After the plaintiff's final witness endured more than 6 hours on the witness stand, Chief U.S. District Judge Vaughn R. Walker told him, “You win the long distance award.”

University of California at Davis psychology professor Greg Herek gave a full day of testimony on the nature of being gay. Davis' UC bio states he is “An internationally recognized authority on prejudice against lesbians and gay men, hate crimes and anti-gay violence, and AIDS-related stigma.”

The trial is the first to challenge the constitutionality of a gay marriage ban in a federal courtroom. Specifically, Proposition 8, the gay marriage ban approved by California voters in 2008.

Lawyers in favor of gay marriage have argued that proponents of Proposition 8 approved the measure out of animus towards gay men and lesbians. The defense says limiting marriage to heterosexual unions fosters a stable environment to raise children.

The plaintiffs, a gay and a lesbian couple, each have been denied the right to marry in California because of Proposition 8. Jeffrey Zarrillo, 36, has testified that Paul Katami, 37, is the “love of my life.” Sanda Stiers, 47, said she fell in love with Chris Perry after being married to a man for 12 years without knowing she was a lesbian. She testified that she became a plaintiff in the case because she wants to marry Perry. “I want the discrimination to end and a more joyful part of our life to begin,” she said.

On Friday, Herek testified that being gay was most likely not a choice, and that conversion therapy – the controversial treatment that aims to alter the sexual orientation of gay men and lesbians – has “very limited” effectiveness and the potential to harm individuals.

Lawyers arguing for Proposition 8 pressed Herek for an unequivocal definition of what what it means to be gay. They asked whether sexuality is “clear cut.”

“Do you agree that homosexuality is a multidimensional phenomenon?” lawyer Howard Nelson Jr. asked at one point.

“That's what I think I've been saying for the last few hours,” Herek replied.

Nelson also attempted to suggest that plaintiffs Stiers and Perry had chosen to be gay. He quoted from Perry's statement that after realizing she was attracted to other women, she “adopted that sexual orientation for myself.”

“What she described here is she experienced this attraction as an enduring pattern, and after recognizing this pattern in herself, she adopted [the gay orientation],” Herek responded.

Proponents of Proposition 8 are clearly hedging their bets on the argument that sexuality can be fluid. Therefore, gay people have the choice to return to a heterosexual relationship. The plaintiffs, however, want to move the argument that being gay is an immutable characteristic – like race – that deserves legal protection.

Plaintiff's lawyers will likely rest their case on Monday and turn over the courtroom to the defense.

The defense's portion of the trial will likely be short. Two-thirds of the defense's original set of expert witnesses withdrew after Walker green lit a plan to broadcast the proceedings to other courtrooms and the Internet. Proposition 8 supporters appealed the ruling to the Supreme Court, which blocked the broadcasts.

Judge Walker has said he will hear closing arguments at a later date, possibly in February. Walker's schedule shows he is unavailable starting on Wednesday.