Last week, an appellate court ruling in a case pertaining to a transgender woman paved the way for California to recognize same-sex marriages from other states.

Thanks to Somers v. Superior Court, California could now be legally bound to recognize same-sex marriages performed out of state – even if it upholds Proposition 8 (which it’s expected to do).

The case did not deal with same-sex marriage. But, ironically, it will affect it.

Here’s why: Somers is a 68-year-old transgender woman, born in Los Angeles in 1941, at which time her birth certificate indicated her gender as “male.” But by 2005, Somers had undergone sex-reassignment surgery and lived in Kansas.

While most states, following California’s lead in the ’70s, allow transgender persons to change the gender indicated on their birth certificates, Kansas does not. (Nor do Idaho, Ohio or Tennesee.)

So Somers (now Gigi Marie Somers), who had changed her name on her driver’s license and received a new Medicare card reflecting her new name and gender, filed a petition in San Francisco Superior Court for “change of gender and issuance of new California birth certificate.”

But because California law requires petitioners to be residents of this state, the judge rejected her petition.

Somers appealed. And, last week, the California Court of Appeal struck down the residency requirement, concluding it violated equal protection. In short, the court found that the statute precluded non-residents from returning to California to change their birth certificates. It said the statute favored California residents over non-residents, which it could find no reason for doing.

What does this have to do with same-sex marriage?

For same-sex marriage advocates, the court’s rationale is key. The court said the statute burdened the “constitutionally guaranteed right of interstate travel” without a compelling reason for doing so. This means that the statute in effect punishes a person born in California who undergoes a gender change and lives in another state; it prevents that person from seeking a change in gender on the birth certificate, simply because the person no longer resides in California.

The ruling will affect future cases involving same-sex marriage, because although we expect the California Supreme Court to uphold Proposition 8, GLBT Californians will still travel to other states to marry. California, arguably, will have to recognize the marriages when they return.

Certainly this will be the case if couples living in states that allow their residents to marry – Massachusetts, Connecticut, Vermont, Iowa – move to California.

California will have to recognize the marriages, because not doing so would interfere with the right to interstate travel, a right guaranteed under the federal Constitution.

If the California Supreme Court upholds Proposition 8, it won’t be because the court agrees with it. It will be because the sole issue before the court is whether a simple majority of voters can amend the California Constitution to take away a right (same-sex marriage) that is not specifically guaranteed under our U.S. Constitution.

This is a federal issue, and when a state court rules on a federal issue, it could land before the U.S. Supreme Court. That court might say the federal Constitution does not protect one’s right to marry a person of the same gender, which would be awful, but while the U.S. Supreme Court has protected gays and lesbians under some circumstances (criminal law), it has not done so with respect to marriage.

Yet a ruling in our favor might not be good either. That’s because polling shows more than two-thirds of the states would vote for the amendment.