In 1999 apartheid's last leader, FW de Klerk, explained to me his motivation for writing an autobiography. "I wanted people to look at our history in its proper time frame. The same mistakes that we made were still being made in the United States and the ex-colonies. Then we carried them on for around 20 years longer. It was a time when we thought it would go away."

De Klerk talked a lot of nonsense that morning, comparing South African apartheid to the EU and insisting it was him, not Nelson Mandela, who ushered in non-racial democracy.

But on the subject of "history's time frame" he was on point. For most of the last century, apartheid was not the exception of one nation but the rule for much of the world that described itself as "civilised". On 1 February 1960 17-year-old Franklin McCain and three black friends went to the whites-only counter at Woolworths in Greensboro, North Carolina, and took a seat. "The day I sat at that counter I had the most tremendous feeling of elation and celebration," he says.

Two days later, the British prime minister Harold Macmillan addressed the South African parliament in Cape Town with an ominous warning. "The wind of change is blowing through this continent," he said. "Whether we like it or not, this growth of national consciousness is a political fact." They didn't like it. But it happened anyway.

In the three years between Macmillan's speech and King's "I have a dream speech", Togo, Mali, Senegal, Zaire, Somalia, Benin, Niger, Burkina Faso, Ivory Coast, Chad, Central African Republic, Democratic Republic of Congo, Gabon, Nigeria, Mauritania, Sierra Leone, Tanganyika and Jamaica all became independent.

Non-racial democracy is a relatively new idea to the west; racism is not. The notion that the people should govern may have been around since ancient Greece, but throughout that time the issue of who counts as people has been continually contested and episodically reassessed.

Last week the US supreme court reassessed the nation's history of voter exclusion and decided the contest was over. The court gutted a key element of the 1965 voting rights act, which demanded that areas with a history of racial discrimination at the polls get prior authorisation before changing their election or voting laws. "There is an old disease, and that disease is cured," argued Bert Rein, when opposing the act before the court earlier this year. "That problem is solved." Justice Roberts agreed, arguing that the provisions were based on "40-year-old" facts.

It's difficult to imagine a less propitious week for that argument. No sooner had the court pronounced racism dead than its skeleton emerged from cupboards galore and started doing the can-can on primetime.

The day before the ruling, the trial of George Zimmerman opened in Florida. Zimmerman, who is Latino, shot dead an unarmed black teenager, Trayvon Martin, claiming he looked "suspicious". He was neither charged nor arrested for several weeks, and then only after nationwide protests. Zimmerman, who had never met Martin, referred to the boy as a "punk" and complained to the police dispatcher: "They always get away." Zimmerman weighs 250lbs and had a 9mm handgun; Martin, 17, weighed 140lbs and had a packet of Skittles and a can of iced tea. Zimmerman claims he was acting in self-defence. "He shot him for the worst of all reasons," said state prosecutor John Guy in his opening statement. "Because he wanted to.''

The day after the ruling, celebrity chef Paula Deen went on the Today show and wept over accusations of racial and sexual harassment that are destroying her empire. In a lawsuit a former employee accuses Deen, among other things, of demanding a "true southern plantation-style wedding" for her brother Earl "Bubba" Heirs in 2007. "Well, what I would really like is a bunch of little niggers to wear long-sleeve white shirts, black shorts and black bow ties," she allegedly said. "You know in the Shirley Temple days, they used to tap dance around."

Since neither Deen nor Zimmerman have been convicted of anything, it should be emphasised that for now they are both innocent. Nonetheless, the allegations and the debates they have provoked provide salient illustrations of the supreme court's folly. I will concentrate on just two.

First, facts that are 40 years old are still facts, and 40 years is not a long period of time when dealing with a centuries-old problem. Apartheid, whether in the US or elsewhere, is a recent phenomenon. Its direct beneficiaries and victims are still alive. Roughly one in five Americans were born after the voting rights act was passed. Deen, who was raised in the deep south, was married that year.

On the rare occasions when my six-year-old son asks questions about the civil rights era, I can point him to his grandparents, who lived through it into adulthood. Nor are its defenders part of some bygone age. Even as the lofty eulogies are prepared for an ailing Nelson Mandela we should not forget that former US vice-president Dick Cheney branded him the leader of a terrorist group in 1986 and the year before his release David Cameron went on a sanctions-busting trip paid for by pro-apartheid lobbyists.

Second, segregation has a legacy – not least because it was so recent. Quashing racist laws does not eliminate racism, only its explicit and codified enforcement. The past has consequences that directly impact the present. History does not just stop because a memory is inconvenient.

The gap between black and white unemployment in the US is roughly the same as it was in 1963; the gap in median income is the same as it was in 1975. Zimmerman did not invent his impressions of Martin out of thin air. They emerge from centuries of demonisation and dehumanisation in which black men, by their very existence, are understood as a threat.

In 2005 Gordon Brown trumpeted the values of "tolerance, liberty and civic duty" exported by the British empire; last month the government settled with thousands of Kenyans tortured under colonial rule.

The speed at which some people seek to flee the past seems to have a direct relationship to their desire to distort it and to live in denial about the present. Power has many parents, but the brutality required to acquire it is an orphan.

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