The historic trial over same-sex marriage in California ends on Wednesday, with the case now in the hands of Judge Vaughn Walker, according to media reports.

Walker is being asked to decide whether California voters violated the U.S. Constitution's guarantees of due process and equal protection when they passed a referendum in November 2008 to amend the state constitution, defining marriage as between a man and a woman.

Attorney Charles Cooper, arguing on behalf of Proposition 8 backers, maintained that society is entitled to reserve its approval of marriage for those who can naturally conceive children.

"The marital relationship is fundamental to the existence and survival of the race," Cooper said in closing arguments before a packed San Francisco courtroom.

The reason the state regulates marriage, he said, is to steer "procreative sexual relationships" into a stable family environment so that children can be raised by their biological parents.

Cooper's counterpart, former U.S. solicitor general Theodore B. Olson, told Walker that the times called for boldness.

Representing two same-sex couples who want to marry, Olson invoked groundbreaking Supreme Court civil rights decisions, such as Brown v. Board of Education, which forbade racial segregation in public schools, and Loving v. Virginia, which threw out that state's law against interracial marriage.

"Proposition 8 discriminates on the basis of sex the same as Virginia law discriminated on the basis of race," Olson said.

The case is likely headed for the U.S. Supreme Court no matter how District Court Chief Judge Vaughn Walker rules on the ban. A decision there could determine the fate of same-sex marriage in the United States for years.

California voters approved the ban known as Prop 8 in 2008, dismaying gay advocates and their allies who had hoped the trend-setting state would side with them.

However U.S. voters in state referendums across the nation have consistently opposed same-sex marriage. It is legal in only five states and the District of Columbia due to court and legislative action.