When my parents tied the knot in the mid-Sixties their respective families were more than a little shocked. My dad is a dark-skinned Pakistani who came to England to study, my mum an auburn-haired, freckled lass from the Welsh valleys. Few of the prospective in-laws approved of the marriage, although both sides of the family were eventually reconciled to the idea, particularly when my parents started having super-cute children (their second son was, apparently, particularly cuddly). In the meantime, my parents faced an uphill and rather daunting struggle for social acceptability.
In many ways, they were the lucky ones. If interracial couples in Sixties Britain faced everything from ghoulish curiosity to downright hostility, American couples faced a period in the slammer. Marrying across the racial divide went by the ugly term 'miscegenation' and was a criminal offence in 16 states including Florida, Texas and Oklahoma. Southern attitudes were perhaps best summed up by a judge passing sentence on a mixed-race couple in 1961: "Almighty God created the races white, black, yellow, Malay and red, and he placed them on several continents. But for the interference with his arrangement there would be no cause for such marriages." They were ordered to leave the state for 25 years or face 12 months in prison.
Such sentiments were not the exclusive preserve of rednecks: they existed among northern liberals, too, something satirised marvellously in the 1967 classic Guess Who's Coming to Dinner, in which a black doctor, played by Sidney Poitier, gets engaged to a white student whom he meets on holiday. The many ironies of racial identity are captured in an unforgettable sequence when Poitier meets the parents (spellbindingly played by Spencer Tracy and Katharine Hepburn) who, despite impeccable liberal credentials, are visibly shocked when they come face to face with their prospective son-in-law. "Mom," the daughter says in surprise, "he thinks you are going to faint because he is a Negro!"
But if the atavistic reactions and social paradoxes of the Sixties and Seventies seem like ancient history, it is worth remembering that they formed the backdrop of daily existence for the sprinkling of mixed-race kids who grew up in that transformative era: Barack Obama was born to a Kenyan father and white mother in Hawaii in 1961, and spent much of his childhood in racially divided America, albeit in ethnically mixed Hawaii. Paul Boateng, the former British Cabinet Minister, was born to a Ghanaian father and Scottish mother. A new generation of mixed-racers include Tiger Woods (mixed-race father and mother), Lewis Hamilton (Afro-Caribbean father and white mother), Zadie Smith (English father and Jamaican mother) and Malcolm Gladwell (English father and Jamaican-born mother).
In almost every measure of social progress. mixed-race kids fare somewhere between whites and blacks (blacks, incidentally, continue to fare significantly worse than whites in everything from income to life expectancy), but there is one area where they shoot off the scale - risk-taking. It does not take a huge leap of imagination to understand why.
As Roland Fryer, a Harvard economist, puts it: "Mixed race adolescents - not having a natural peer group - need to engage in risky behaviour to be accepted." This is not to imply that all mixed-race teenagers are afflicted by a sense of divided identity, but merely that, at a population level, there are measurable and often dramatic consequences - which may explain the emergence of mixed-race high-flyers. Although interracial marriages are more common today than in the Sixties, they remain surprisingly rare, particularly in the United States where just 1 per cent of white marriages and 5 per cent of black marriages are across the racial divide. The rarest kind of interracial marriage is between white men and black women; the most common is between white men and Asian women. In the UK things are moving faster, largely because communities are much less ghettoised.
According to a report by the Equality and Human Rights Commission, published yesterday, half of men and a third of women with Caribbean heritage who are in couples are with partners of a different race. But this drops to well under 10 per cent of Bangladeshi men and women.
While racial mixing is increasing only gradually in global terms, the trend has provoked some dramatic predictions. In a speech last year, Steve Jones, Professor of Genetics at University College London, argued that we will soon witness the complete obliteration of the races: "Worldwide, all populations are becoming connected," he said. "History is made in bed, but nowadays the beds are getting closer together. We are mixing into a global mass, and the future is brown."
This is one of the less talked-about consequences of globalisation and is the outcome that anti-miscegenation laws (finally struck down by the US Supreme Court in 1967) were designed to avoid. Although this vision is still a long way off, it is worth asking how you feel about the prospect of a mongrelised human future: does it fill you with horror or excitement (or possibly both)?
Before answering this question, try this one instead: what is race? In the census data, it is defined by self-identity: you are given a choice of boxes to tick - mixed race became a category in the UK only in the last census of 2001 - and the statisticians take it from there. You might suppose that this is a time-saving device and that a clever scientist could give you a definitive classification with a blood test or a mouth swab, but you would be wrong. One of the most striking things to emerge from the human genome project is that the human species is, genetically speaking, remarkably uniform and that the little genetic variation that exists is found within population groups (about 90 per cent) as opposed to between population groups (around 10 per cent). The categories that we call races blend seamlessly into each other and have no genetically defined boundaries.
Why? Because, until very recently, all humans lived together in Africa (yes, we all have African roots). The migration of our ancestors into the rest of the world probably happened only within the past 70,000 years, so natural selection has had very little time to get to work on driving the continental groups apart. The differences that do exist, such as skin colour and nose shape, are, genetically-speaking, superficial.
As Henry Harpending, the American geneticist, put it, humans are a bit like PCs: "Computers are divisible into major races - Compaq, Dell, Gateway, Micron - as well as many minor populations. These computer races are like human races. Are there deep essential differences? Hardly. Take the cases off and we can barely tell them apart. The components of PCs are commodities that are completely interchangeable. Human race differences are like that." In other words, the differences between the races are many times greater if we look at the label than if we look inside. That is not to say that there are no genetic differences at all, but that they are small on-average differences. When meeting someone new, it makes sense to judge them on their abilities rather than their label.
But this is easier said than done. The problem is that we make label judgments and it is this, I think, that helps to explain why gaping divisions continue to exist between the races on everything from income levels to marital intimacy, and why mixed race kids feel the need to take big risks to be accepted. If you think that you are immune to such judgments it might be worth checking out the Harvard Implicit Association Test website: you might be surprised - rather as Spencer Tracy and Katharine Hepburn were in Guess Who's Coming to Dinner at what your subconscious is really like. I rated as having a strong automatic preference for European Americans compared to African Americans, since you ask.
This is not a case of bigotry but of psychology. Our brains, seeking to make sense of the complexity of the world, instinctively divide things into categories to speed up processing. It makes computational sense to make crude generalisations about minority groups - this is why we find it more difficult, for example, to discern facial differences in other races that are perfectly obvious within our own (they all look the same to me). But these biases break down with familiarity. One study showed that something as trivial as watching basketball (which has many African American players) caused whites to be much better at recognising black faces.
This is why mixed-race kids should not be seen as evidence of a looming racial apocalypse but as the reproductive consequences of a rather uplifting kind of barrier-breaking. According to Ludi Simpson, Professor of Population Studies at Manchester University, integration tends to have a beneficial impact on the prevalence of racism. Local surveys indicate that most people regard racial integration as benign when it happens in their own backyard. It is only when they are asked about racial integration more generally that the responses tend to be negative, largely because the media tends to exaggerate the issue.
The barriers between human population groups never had much basis in genetics, but were constructed from feelings of unfamiliarity. In this sense, the likes of Obama, Hamilton and Woods are the poster boys for a new and exciting type of globalisation. We usually look to governments to solve the problems of the world; in this case, we should also look to bedrooms.
Mixed race doesn't mean fitter
In some quarters, there is a belief that mixed-race individuals are genetically fitter than those born to parents of the same race. Being fitter in this sense means that you have a head-start in the reproductive stakes because you are more beautiful (and so find a mate more easily) and/or because you are healthier (and thus will have children more likely to survive to breeding age).
This "hybrid vigour" argument - the term is usually applied to plants - can be thought of as the polar opposite to inbreeding. If inbreeding is bad, then the blending of two dramatically different gene pools must, the theory goes, lead to genetic nirvana. Such theories are hinted at in comments about the attractiveness of mixed-race people; they were espoused more fully in Alon Ziv's controversial book Breeding Between the Lines: Why Interracial People are Healthier and More Attractive.
And they are seemingly confirmed by the success of 'mutts' such as Barack Obama, Tiger Woods and Lewis Hamilton.
The theory, however, does not stand up to real scrutiny. Inbreeding does indeed bring problems; infants born to first-cousin marriages have a higher than average rate of congenital heart problems. In Britain, children of Pakistani origin are disproportionately affected by certain genetic disorders, thought to arise from the culture of consanguineous marriages (between close relatives). On the other hand, health studies also show that there are no startling benefits accruing to children of mixed parentage.
Overall, the rate of birth defects among mixed-race babies seems to be the same as for other babies, reinforcing the idea that, while people might come in different coloured envelopes, the contents are not that genetically distinct.