Posted on October 22, 2019

Twin Study That Was to Prove Arthur Jensen Wrong Proves Him Right

Richard Lynn, American Renaissance, March 1994

It is now about a quarter of a century since Arthur Jensen of the University of California at Berkeley broke the consensus of some forty years by proposing that there is a strong genetic basis to race differences in intelligence.1 From around 1930 it had been almost unanimously stated that the IQ difference between blacks and whites was entirely due to social deprivation. This was the doctrine routinely taught to college students throughout the United States.

During this period of virtually unchallenged environmentalism it was nevertheless recognized that there was a substantial IQ difference between American blacks and whites. This was first shown conclusively during the First World War when conscripts to the military were given intelligence tests to determine whether they were acceptable for service and what training they should be given. The average IQ difference between blacks and whites was 17 points, and this difference had been shown repeatedly in later studies. The difference has never been in dispute. The problem lies in its causes and what part, if any, genetics plays.

It was in 1969 that this environmentalist consensus was broken by Dr. Jensen. He suggested that the best reading of the evidence was that between two thirds and three quarters of the black IQ deficit was probably due to genetic causes. What this meant was that if black children were reared in the same environment as whites, the IQ difference would be reduced to between two thirds and three quarters, i.e. to about 10-12 IQ points. At the time, this was essentially an informed guess. There was no direct evidence to show whether it was right or wrong.

The crucial evidence on this question became available only in 1992, and it showed that Dr. Jensen was right and, if anything, had underestimated the strength of the genetic factor. Ironically, the evidence was produced in a study that was designed to prove that Dr. Jensen was wrong but ended up showing he was right.2 This is the story.

The Adoption Study

In the early 1970s, Sandra Scarr of Harvard and her collaborator Richard Weinberg decided to study what would happen to the intelligence of black babies who were adopted and brought up by white parents. Their plan was to test Dr. Jensen’s hypothesis that there would still be a substantial deficit in their intelligence. Dr. Scarr and Dr. Weinberg were confident that this hypothesis would be disproved and that the IQ of the black children would turn out to be the same as that of white children.

They found 29 black infants adopted at an early age by white college graduates. They also found 68 babies with one black and one white parent, which they called the inter-racial children, who had also been adopted by white college graduates. And finally, as controls, they found 25 white adopted babies.

The first report on what came to be known as the Minnesota Transracial Adoption Study came out in 1976.3 At this time the white adopted children were ten years old while the black and inter-racial children were six. The average IQs of the three groups were black = 97, inter-racial = 109, and white = 111.

Dr. Scarr and Dr. Weinberg claimed this result as a triumph for environmentalists. As everyone knows, they argued, the average black IQ in the United States is 85. The average of the black infants brought up by white parents was 97, almost the same as the white average of 100. Furthermore, the IQ of the inter-racial children was 109, well above that of whites. It seemed that being brought up by white college graduates had removed the black IQ deficit. Dr. Scarr and Dr. Weinberg claimed they had proved the environmentalist case. It seemed Dr. Jensen was wrong.

At the time, these conclusions were fallacious but they were to be shown to be even more fallacious in 1992 when the second report on the study was published. There were two fallacies in the study. First, the babies came from the northern states and northern blacks have a higher average intelligence than southern blacks. The probable reason for this is that more intelligent blacks migrated north, leaving the less intelligent in the south. The average IQ of northern blacks is 88 while that of southern blacks is 83, so the IQ of 97 for the adopted blacks must be compared with the figure of 88 for northern blacks who are reared in their own black environments. Even so, they apparently had a nine IQ point advantage, suggesting that being reared by white parents raises the black IQ by nine points.

This conclusion needs further modification. The children were mostly tested with the Wechsler Intelligence Scale for Children (the WISC), which was constructed and standardized in 1947. The intelligence level of the population has been increasing over time at about 3 IQ points a decade, largely because of improvements in nutrition.4 Dr. Scarr and Dr. Weinberg were therefore using a test that was 29 years out of date.

Over that period the average IQs of both blacks and whites rose by nine points. So where does this leave the apparent 9-point advantage gained by black children raised by white parents. The answer is “precisely nowhere.” The average IQ of these children turns out to be just the same as that of black children raised by their own parents. This would have been clear if Dr. Scarr and Dr. Weinberg had used an up-to-date IQ test.

Nevertheless, the inter-racial children appeared to perform a bit better. On the genetic hypothesis they should have obtained an average IQ half way between whites and blacks. Adjusting for the fact that IQs are higher in the northern states (blacks = 88, whites = 103), and adding 9 IQ points for the outdated test norms (blacks now = 97, whites now = 112), the IQ of the inter-racial children should have been half way between 97 and 112, or 104.5. The fact that their IQ was 109 seems to show that these children had gained 4.5 IQ points from having been reared in a white family. This suggests that being brought up by college-educated white parents does improve the IQs of inter-racial children.

The Follow-up Study

This result gave some support to the environmentalist position, but even this consolation was to disappear when a follow-up study of the children was published in the fall of 1992. The children were given intelligence tests again in 1986, at an average age of 17 years. It was to be six years before Dr. Scarr and Dr. Weinberg published the results. Normally these data would take a month or two to analyze and write up and a year to publish, and the results would have appeared in 1988. The four-year publication delay is excessive and is probably due to the fact that Dr. Scarr and Dr. Weinberg were worried by what they found.

The results showed that adoption had no beneficial effect whatever on the IQs of the black, inter-racial, or white children. Their average IQs at age 17 were 89 (black), 98 (inter-racial), and 106 (white). Different IQ tests were used from those in the earlier 1976 report, but they were still approximately 10 years out of date. Three points must therefore be added to the average IQ of the group to which the black children are compared — blacks in the northern states.

The IQ of northern blacks (adjusted up by three points) was 91 in 1986, so the black adopted children actually had lower IQs (89 vs 91) than northern blacks brought up in their own communities. The same absence of any effect is found for the inter-racial and white children after adjustments are made for the fact that the children were from northern states and that the test norms were obsolete.

Note also that the difference between the reported (unadjusted) IQs of black and white children reared in identical environments is 18 points (88 vs 106), slightly greater than the average difference between blacks and whites that has consistently been found since the First World War. Even if adjustments for obsolete test norms and northern origin of the children were not necessary or appropriate, this 18-point difference is very difficult for environmentalists to explain. If rearing environment rather than race accounts for racial differences in IQ, why do these differences remain even when the rearing environment is the same?

There is only one conclusion to be drawn from these results: being adopted by white college graduates has no beneficial effect whatever on the intelligence of black, white or inter-racial children at the age of 17. Since the results show that the rearing environment has no effect on the IQs of adopted children, the only conclusion to be drawn is that the factors responsible for these different levels of IQ are genetic. Not only do they vindicate the conclusion put forward by Dr. Jensen in 1969. They show that Dr. Jensen underestimated the genetic contribution to the low black IQ. The study by Dr. Scarr and Dr. Weinberg indicates that genetic factors are responsible for the entire black IQ deficit, not for between two-thirds and three-quarters of it as Dr. Jensen had suggested.

Curiously, in their paper Dr. Scarr and Dr. Weinberg state that their results “demonstrate the strong effects of the rearing environment on IQ.” Their results provide no evidence whatsoever for this statement. Apparently, the wish was father to the thought.

Policy Implications

Now that the genetic basis for the low level of black intelligence is established it is important to start thinking about the social and political implications of this problem. We have to face the fact that because intelligence is an important determinant of educational and occupational achievement, blacks are never going to achieve equality with whites. This can only mean that the social problems and tensions arising from black underachievement are going to continue into the indefinite future. These problems consist of a substantial black underclass characterized by unemployment, welfare dependency, crime and drug addiction.

Furthermore, this underclass will increase in size, partly through high fertility and partly through immigration. The Census Bureau estimates that the black population of the United States will increase by 25 percent over the next 60 years.5

Both sources of increase need to be addressed. The fertility of the underclass needs to be reduced by the provision of family planning instruction and services, and the removal of welfare incentives. Immigration needs to be reduced to zero, as is now the case throughout Europe. The claims of bogus political refugees should be scrutinized more rigorously and greater numbers should be refused admission. Illegals need to be identified more effectively and repatriated. None of these policies will be easy to implement, but these are the issues which need to be opened up for public discussion.

1. A.R. Jensen. How much can we boost IQ and scholastic achievement? Harvard Educational Review, 39, 449-483.

2. R.A. Weinberg, S. Scarr & I.D. Waldman. The Minnesota transracial adoption study: a follow up of IQ test performance at adolescence. Intelligence, 1992, 16, 117-135.

3. S. Scarr and R.A. Weinberg. IQ test performance of black children adopted by white Americans. American Psychologist, 1976, 54, 260-267.

4. R. Lynn. The role of nutrition in the secular increase of intelligence. Personality and Individual Differences, 1990, 11, 273-286.

5. J. Day. Population Projections of the United States by Age, Sex, Race and Hispanic Origin: 1992–2050. Washington, D.C.: Bureau of the Census.