The state of Michigan's first witness in a challenge to the state's gay marriage ban was thrown out on Monday.

U.S. District Judge Bernard Friedman said that Sherif Girgis, a Princeton-educated philosophy expert and co-author of What is Marriage? Man and Woman: A Defense, had nothing to offer the case.

“He's very eloquent … but right now, all he is offering to us is mainly his opinions,” Friedman said of Girgis. “The court does not believe … that he should be allowed to testify.”

Attorneys for the plaintiffs, a lesbian couple wishing to marry so that they may jointly adopt their three foster children, argued that Girgis is not a lawyer, child development expert, psychologist or expert in Michigan law.

Testimony heard during the trial's first week looked at gender roles and procreation as each relates to marriage. Experts testified that children need good parents, regardless of sexual orientation or gender.

(Related: Michigan gay marriage trial looks at gender roles, procreation.)

The state's first witness, Mark Regnerus, an associate professor of sociology at the University of Texas at Austin, testified for more than three hours.

Regnerus is the lead author of a widely criticized 2012 study which concluded that children are negatively affected by having gay parents. The study was funded by the socially conservative New Jersey-based Witherspoon Institute.

While Regnerus has acknowledged that his study did not include children raised by gay couples in a stable relationship, he defended his work and insisted that the state was right in questioning whether gay couples make good parents.

“Until we get more more evidence, we should be skeptical,” Regnerus said. “It's prudent for the state to retain its definition of marriage to one man, one woman.”

Last month, Regnerus told a university audience that allowing gays to marry will lead to straight men demanding open relationships.

Lawyers for the plaintiffs will cross-examine Regnerus on Tuesday.

Meanwhile, Oakland County Clerk Lisa Brown on Monday said that if Friedman overturns the ban, her office would immediately start issuing marriage license to gay couples, the Detroit Free Press reported.