The plaintiffs side in the legal challenge to California’s ban on same-sex marriage concluded on Friday, offering a final expert who spent a full day on the witness stand engaged in a debate over whether homosexuality is a product of nature or choice.

Gregory Herek, a University of California at Davis psychology professor, testified that research for the most part sides with the theory that gays and lesbians have no choice in their sexual preference, a position confronted for more than five hours by a lawyer defending Proposition 8.

The testimony went to a central competing theme in the standoff over gay marriage. Same-sex couples seeking the right marry maintain that homosexuality is an inherent characteristic, a factor that should extend constitutional protections to them as a minority group facing discrimination. Foes of same-sex marriage insist homosexuality is a social choice, not a biological characteristic deserving of the highest legal protections.

Read the rest of Howard Mintz’s San Jose Mercury article here.