Our friend Kevin had to cancel a lunch date with Steve the other day. He was taking one of his twin sons to the doctor.

That’s an unremarkable event except for one thing: Kevin is gay, and he and his partner saved for many years to afford a surrogate mother. Concern for a sick child is not limited to heterosexual couples who conceive their offspring in the traditional way.

That small story helps explain why public attitudes toward gay marriage are shifting so rapidly. Almost four out of five Americans say they have a close friend, relative or co-worker who is openly gay, according to USA Today. Many Americans know same-sex couples who are raising their kids with the same affection, and anxiety, as any straight parents. And they know they are seeing family values in action.

Later this month, the U.S. Supreme Court will hear arguments in two landmark cases concerning gay marriage. One challenges California’s Proposition 8, an initiative passed in 2008 that limits marriage to a man and a woman. The other seeks to overturn the Defense of Marriage Act (DOMA), which bars the federal government from recognizing same-sex marriages even when they’re legal under state law.

Justices don’t commission polls before they decide cases, but they don’t live in a political vacuum, either. Public opinion can influence their judgment, and recent surveys all agree: More than half of all Americans now support legalizing gay marriage. Last month, for example, CBS News reported that 54 percent agree with the statement that “it should be legal … for same-sex couples to marry,” while 39 percent disagreed. That is a jump of eight points in favor of legality in less than a year.

More significantly, there is a huge age gap on the issue. Gallup found that 73 percent of voters younger than 30 support same-sex unions, and the political world is already responding to those numbers. Three states legalized gay marriage last November, bringing the national total to nine, plus the District of Columbia; others are likely to follow. The Rev. Martin Luther King Jr. could have been speaking of gay marriage when he said in another context, “The arc of history is long, but it bends toward justice.”

As Republican strategist John Feehery told The New York Times: “The ground on this is obviously changing, but it is changing more rapidly than people think.” Added Steve Schmidt, an adviser to John McCain’s 2008 campaign: “The die is cast on this issue when you look at the percentage of young voters who support gay marriage.”

Attention has focused on Mitt Romney’s dismal performance among racial minorities, but the GOP’s unpopularity among young voters is just as threatening to the party’s future.

Barack Obama won 71 percent of the Latino vote, but his margin rose to 74 percent among Latinos younger than 30. The Democrats won 51 percent of the overall national vote but 60 percent of the youth vote.

It’s hard to measure the precise impact of gay rights, but clearly the issue helped Obama and hurt Romney with the younger set. The same can be said for women. Obama lost the male vote by seven points but won the female vote by 11, and women are significantly more likely to support gay marriage than men.

Of course, Democrats have long done better with young and female voters. No surprise there. What is surprising is the growing support for gay marriage among two other groups — Republicans and business executives. Ken Mehlman, a former chairman of the Republican National Committee, organized dozens of prominent GOP’ers to sign a friend-of-the-court brief supporting gay marriage and opposing the California initiative.

“We are trying to say to the court that we are judicial and political conservatives, and it is consistent with our values and philosophy for you to overturn Proposition 8,” explains Mehlman, who is openly gay.

A similar brief signed by more than 100 corporate leaders asked the court to jettison the Defense of Marriage Act. “We want to show the perspective that DOMA is bad for business,” Joshua Rosenkranz, a lawyer who helped write the brief, told the Times. “It undermines teamwork and efficiency and causes needless distractions. I wanted to … demonstrate that corporate America embraces equality.”

Yes, a shrinking group of sincere Americans still believes that gay marriage is morally wrong and threatens traditional values. But the facts contradict them. Theology cannot compete with reality. Marches and protests are fine, but the real revolutionaries are the gay parents taking their kids to the doctor. Every day. Just like everyone else.

(Steve and Cokie Roberts can be contacted by email at stevecokie@gmail.com.)