There were 784,764 U.S. residents who described their race as white and black in the last census count. But that number didn’t include Laura Martin, whose father is black and mother is white.

“I’ve always just checked black on my form,” said Martin, a 29-year-old university employee in Las Vegas. She grew up surrounded by black family and friends, listening to black music and active in black causes — “So I’m black.”

Friday was the deadline to mail 2010 census forms, the once-a-decade count of the American population. Although the results are expected to show an increase in the number of multiracial people, some African-Americans with one white parent are deciding to simply “stay black.”

This is only the second census to allow people to identify themselves by more than one race. About 7 million people, or 2.4 percent of the U.S. population, chose that option in 2000.

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It’s impossible to know how many of the 35 million people counted as “black alone” in 2000 have a white parent. But it’s clear that the decision to check one box — or more — on the census is often steeped in history, culture, pride and mentality.

Exhibit A is President Barack Obama. He declined to check the box for “white” on his census form, despite his mother’s whiteness.

Obama offered no explanation, but Leila McDowell has an idea.

“Put a hoodie on him and have him walk down an alley, and see how biracial he is then,” said McDowell, vice president of communications for the National Association for the Advancement of Colored People.

“Being black in this country is a political construct,” she said. “Even though my father is white and I have half his genes, when I apply for a loan, when I walk into the car lot, when I apply for a job, they don’t see me as half white, they see me as black. If you have any identifying characteristics, you’re black.”

There is evidence, though, that while some may be resistant to the idea of identifying as multiracial, white attitudes are moving in that direction. In a January poll by the Pew Research Center, 53 percent of white people said Obama is “mixed race” and 24 percent said he is black. In contrast, 55 percent of black people said Obama is black and 34 percent said he is mixed.

This also may represent a new twist on the “one drop” concept, which for centuries held that even one black ancestor made a person black. Now a brown-skinned man is president, and for many white people, one white parent means you are not black.

But the logic is simple for Ryan Graham, the brown-skinned son of a white-black marriage who defines himself as multiracial.

“Say you’re wearing a black-and-white shirt. Somebody asks, ‘What color is your shirt?’ It’s black and white. There you go. People ask me, ‘What race are you?’ I say I’m black and white. It’s that simple,” said Graham, a 25-year-old sales consultant from Fort Lauderdale, Florida.

Graham’s mother founded Project Race in 1991 to fight for a multiracial classification in the census. Graham testified before Congress on the issue when he was 8. He’s disappointed that Obama chose not to check the white box on the census, but said that people should be allowed to define themselves however they choose.

“It’s frustrating from a point that there’s a lot of multiracial people out there who see Obama out there doing that, knowing that he’s multiracial, and they think maybe that’s the right choice. But there’s a lot of people saying maybe it’s the wrong choice.”

For those who decline to check the white box: “Think about your family, think about what makes you you,” Graham said. “How you are, who you are, where you come from.”

Most experts say there is very little genetic difference between people of different races — as little as 1 percent. “Race is a social concept, not a scientific one,” goes a much-repeated quote from J. Craig Venter, who led one of the first projects to decipher the entire human genome.

That’s one reason why the American racial system is “facing taxonomical meltdown,” said Nell Painter, a Princeton University history professor and author of “The History of White People.”

“The complications of the classification system, the resistance that people are mounting, the weight of immigration and marriage mixing, young people are checking more than one box,” Painter said. “The system might just all fall away.”

Which would leave blackness to be defined person by person, according to how they think, the way they look at the world — blackness as a state of mind.

Tony Spearman, author of “Why Am I Black,” was born to two white parents. He grew up in a mostly black town, worked at a historically black college, taught physics to predominantly black students.

On every census since 1996, Spearman has marked one box: black.

“My wife got angry at me, my father got angry at me,” said Spearman, 42. “They told me, ‘You gotta be truthful!’ I said, ‘I am!’ … Race is a foolish thing. It has nothing to do with our humanness.”

“The system is breaking down, and I hope it continues to break down,” Spearman said. “Because when it fully breaks down, we’ll start to measure people by the content of their hearts.”

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Jesse Washington covers race for The Associated Press. He has one white parent and one black, and did not check “white” on the census. Reach him at jwashington@ap.org or www.twitter.com/jessewashington.

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