A few years ago the late Richard Herrnstein and I published a controversial book about IQ, The Bell Curve, in which we said that much would depend on IQ. On average, the bright children from such families will do well in life - and the dull children will do poorly. Unemployment, poverty and illegitimacy will be almost as great among the children from even these fortunate families as they are in society at large - not quite as great, because a positive family background does have some good effect, but almost, because IQ is such an important factor.
"Nonsense!" said the critics. "Have the good luck to be born to the privileged and the doors of life will open to you - including doors that will let you get a good score in an IQ test. Have the bad luck to be born to a single mother struggling on the dole and you will be held down in many ways - including your IQ test score." The Bell Curve's purported relationships between IQ and success are spurious, they insisted: nurture trumps nature; environment matters more than upbringing.
An arcane debate about statistical methods ensued. Then several American academics began using a powerful, simple way of testing who was right: instead of comparing individual children from different households, they compared sibling pairs with different IQs. How would brothers and sisters who were nurtured by the same parents, grew up in the same household and lived in the same neighbourhood, but had markedly different IQs, get on in life?
The research bears out what parents of children with unequal abilities already know - that try as they might to make Johnny as bright as Sarah, it is difficult, and even impossible, to close the gap between them.
A very large database in the United States contains information about several thousand sibling pairs who have been followed since 1979. To make the analysis as unambiguous as possible, I have limited my sample to brothers and sisters whose parents are in the top 75 per cent of American earners, with a family income in 1978 averaging £40,000 (in today's money).
Families living in poverty, or even close to it, have been excluded. The parents in my sample also stayed together for at least the first seven years of the younger sibling's life.
Each pair consists of one sibling with an IQ in the normal range of 90-110 ,a range that includes 50% of the population. I will call this group the normals. The second sibling in each pair had an IQ either higher than 110, putting him in the top quartile of intelligence (the bright) or lower than 90, putting him in the bottom quartile (the dull). These constraints produced a sample of 710 pairs.
How much difference did IQ make? Earned income is a good place to begin. In 1993, when we took our most recent look at them, members of the sample were aged 28-36. That year, the bright siblings earned almost double the average of the dull: £22,400 compared to £11,800. The normals were in the middle, averaging £16,800.
These differences are sizeable in themselves. They translate into even more drastic differences at the extremes. Suppose we take a salary of £50,000 or more as a sign that someone is an economic success. A bright sibling was six-and-a-half times more likely to have reached that level than one of the dull. Or we may turn to the other extreme, poverty: the dull sibling was five times more likely to fall below the American poverty line than one of the bright. Equality of opportunity did not result in anything like equality of outcome. Another poverty statistic should also give egalitarians food for thought: despite being blessed by an abundance of opportunity, 16.3% of the dull siblings were below the poverty line in 1993. This was slightly higher than America's national poverty rate of 15.1%.
Opportunity, clearly, isn't everything. In modern America, and also, I suspect, in modern Britain, it is better to be born smart and poor than rich and stupid. Another way of making this point is to look at education. It is often taken for granted that parents with money can make sure their children get a college education. The young people in our selected sample came from families that were overwhelmingly likely to support college enthusiastically and have the financial means to help. Yet while 56% of the bright obtained university degrees, this was achieved by only 21% of the normals and a minuscule 2% of the dulls. Parents will have been uniformly supportive, but children are not uniformly able.
The higher prevalence of college degrees partly explains why the bright siblings made so much more money, but education is only part of the story. Even when the analysis is restricted to siblings who left school without going to college, the brights ended up in the more lucrative occupations that do not require a degree, becoming technicians, skilled craftsmen, or starting their own small businesses. The dull siblings were concentrated in menial jobs.
The differences among the siblings go far beyond income. Marriage and children offer the most vivid example. Similar proportions of siblings married, whether normal, bright or dull - but the divorce rate was markedly higher among the dull than among the normal or bright, even after taking length of marriage into account. Demographers will find it gloomily interesting that the average age at which women had their first birth was almost four years younger for the dull siblings than for the bright ones, while the number of children born to dull women averaged 1.9, half a child more than for either the normal or the bright. Most striking of all were the different illegitimacy rates. Of all the first-born children of the normals, 21% were born out of wedlock , about a third lower than the figure for the United States as a whole, presumably reflecting the advantaged backgrounds from which the sibling sample was drawn. Their bright siblings were much lower still, with less than 10% of their babies born illegitimate. Meanwhile, 45% of the first-born of the dull siblings were born outside of marriage.
The inequalities among siblings that I have described are from 1993 and are going to become much wider in the years ahead. The income trajectory for low-skill occupations usually peaks in a worker's twenties or thirties. The income trajectory for managers and professionals usually peaks in their fifties. The snapshot I have given you was taken for an age group of 28-36 when many of the brights are still near the bottom of a steep rise into wealth and almost all the dulls' incomes are stagnant or even falling. . . .
The inequalities I have presented are the kind you are used to seeing in articles that compare inner-city children with suburban ones, black with white, children of single parents with those from intact families. Yet they refer to the children of a population more advantaged in jobs, income and marital stability than even the most starry-eyed social reformer can hope to achieve.
You may be wondering whether the race, age or education of siblings affects my figures. More extended analyses exist, but the short answer is that the phenomena I have described survive such questions. Siblings who differ in IQ also differ widely in important social outcomes, no matter how anyone tries to explain away the results. Ambitious parents may be dismayed by this conclusion, but it is none the less true for all that.
A final thought: I have outlined the inequalities that result from siblings with different IQs. Add in a few other personal qualities: industry, persistence, charm, and the differences among people will inevitably produce a society of high inequalities, no matter how level the playing field has been made. Indeed, the more level the playing field, and the less that accidents of birth enter into it, the more influence personal qualities will have. I make this point as an antidote to glib thinking on both sides of the Atlantic and from both sides of the political spectrum. Inequality is too often seen as something that results from defects in society that can be fixed by a more robust economy, more active social programmes, or better schools. It is just not so.
The effects of inequality cannot be significantly reduced, let alone quelled, unless the government embarks on a compulsory redistribution of wealth that raises taxes astronomically and strictly controls personal enterprise. Some will call this social justice. Others will call it tyranny. I side with the latter, but whichever position one takes, it is time to stop pretending that, without such massive compulsion, human beings in a fair and prosperous society will ever be much more equal than they are now.
From the Sunday Times, UK, May 25 1997.
A longer version of this article appears in the summer issue of The Public Interest. Dr. Murray is a fellow at the American Enterprise Institute (1150 17th Street NW, Washington, DC, 20036)