WASHINGTON, USA (AP) – A perplexing new chapter is unfolding in Barack Obama’s racial saga: Many people insist that “the first black president” is actually not black.

Debate over whether to call this son of a white Kansan and a black Kenyan biracial, African-American, mixed-race, half-and-half, multiracial – or, in Obama’s own words, a “mutt” – has reached a crescendo since Obama’s election shattered assumptions about race.

Obama has said, “I identify as African-American – that’s how I’m treated and that’s how I’m viewed. I’m proud of it.” In other words, the world gave Obama no choice but to be black, and he was happy to oblige.

But the world has changed since the young Obama found his place in it.

Intermarriage and the decline of racism are dissolving ancient definitions. The candidate Obama, in achieving what many thought impossible, was treated differently from previous black generations. And many white and mixed-race people now view President-elect Obama as something other than black.

So what now for racial categories born of a time when those from far-off lands were property rather than people, or enemy instead of family?

“They’re falling apart,” said Marty Favor, a Dartmouth professor of African and African-American studies and author of the book Authentic Blackness.

“In 1903, W E B DuBois said the question of the 20th century is the question of the colour line, which is a simplistic black-white thing,” said Favor, who is biracial. “This is the moment in the 21st century when we’re stepping across that.”

Rebecca Walker, a 38-year-old writer with light brown skin who is of Russian, African, Irish, Scottish and Native American descent, said she used to identify herself as ‘human’, which upset people of all backgrounds. So she went back to multiracial or biracial, “but only because there has yet to be a way of breaking through the need to racially identify and be identified by the culture at large”.

“Of course Obama is black. And he’s not black, too,” Walker said. “He’s white, and he’s not white, too. Obama is whatever people project onto him … he’s a lot of things, and neither of them necessarily exclude the other.”

But US Rep G K Butterfield, a black man who by all appearances is white, feels differently.

Butterfield, 61, grew up in a prominent black family in Wilson, NC. Both of his parents had white forebears, “and those genes came together to produce me”. He grew up on the black side of town, led civil rights marches as a young man, and to this day goes out of his way to inform people that he is certainly not white.

Butterfield has made his choice; he says let Obama do the same.

“Obama has chosen the heritage he feels comfortable with,” he said. “His physical appearance is black. I don’t know how he could have chosen to be any other race. Let’s just say he decided to be white – people would have laughed at him.”

“You are a product of your experience. I’m a US congressman, and I feel some degree of discomfort when I’m in an all-white group. We don’t have the same view of the world, our experiences have been different.”

The entire issue balances precariously on the ‘one-drop’ rule, which sprang from the slave owner’s habit of dropping by the slave quarters and producing brown babies. One drop of black blood meant that person, and his or her descendants, could never be a full citizen.

Today, the spectrum of skin tones among African-Americans – even those with two black parents – is evidence of widespread white ancestry. Also, since blacks were often light enough to pass for white, unknown numbers of white Americans today have blacks hidden in their family trees.

One book, Black People and their Place in World History, by Dr Leroy Vaughn, even claims that five past presidents – Thomas Jefferson, Andrew Jackson, Abraham Lincoln, Warren Harding and Calvin Coolidge – had black ancestors, which would make Obama the sixth of his kind.

Mix in a few centuries’ worth of Central, South and Native Americans, plus Asians, and untold millions of today’s US citizens need a DNA test to decipher their true colours. The melting pot is working.

Yet the world has never been confronted with such powerful evidence as Obama. So as soon as he was elected, the seeds of confusion began putting down roots.

“Let’s not forget that he is not only the first African-American president, but the first biracial candidate. He was raised by a single white mother,” a Fox News commentator said seven minutes after Obama was declared the winner.

“We do not have our first black president,” the author Christopher Hitchens said on the BBC programme Newsnight. “He is not black. He is as black as he is white.”

A Doonesbury comic strip that ran the day after the election showed several soldiers celebrating.

“He’s half-white, you know,” says a white soldier. “You must be so proud,” responds another.

Pride is the centre of racial identity, and some white people seem insulted by a perception that Obama is rejecting his white mother (even though her family was a centrepiece of his campaign image-making) or baffled by the notion that someone would choose to be black instead of half-white.

“He can’t be African-American. With race, white claims 50 per cent of him and black 50 per cent of him. Half a loaf is better than no loaf at all,” Ron Wilson of Plantation, Fla, wrote in a letter to the Sun-Sentinel newspaper.

Attempts to whiten Obama leave a bitter taste for many African-Americans, who feel that at their moment of triumph, the rules are being changed to steal what once was deemed worthless – blackness itself.

“For some people it’s honestly confusion,” said Favor, the Dartmouth professor. “For others it’s a ploy to sort of reclaim the presidency for whiteness, as though Obama’s blackness is somehow mitigated by being biracial.”

Then there are the questions remaining from Obama’s entry into national politics, when some blacks were leery of this Hawaiian-born newcomer who did not share their history.

Linda Bob, a black schoolteacher from Eustis, Fla, said that calling Obama black when he was raised in a white family and none of his ancestors experienced slavery could cause some to ignore or forget the history of racial injustice.

“It just seems unfair to totally label him African-American without acknowledging that he was born to a white mother,” she said. “It makes you feel like he doesn’t have a class, a group.”

There is at least one group eagerly waiting for Obama to embrace them. “To me, as to increasing numbers of mixed-race people, Barack Obama is not our first black president. He is our first biracial, bicultural president … a bridge between races, a living symbol of tolerance, a signal that strict racial categories must go,” Marie Arana wrote in the Washington Post.

He’s a bridge between eras as well. The multiracial category “wasn’t there when I was growing up,” said John McWhorter, a 43-year-old fellow at the Manhattan Institute’s Centre for Race and Ethnicity, who is black. “In the ’70s and the ’80s, if somebody had one white parent and one black parent, the idea was they were black and had better get used to it and develop this black identity. That’s now changing.”