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The Role of Genetics in IQ and Intelligence

Your brain, your nervous system, your entire body is constructed according to instructions received from the genes that you have inherited from your parents. It would seem reasonable that superior genes would provide a child with superior intelligence capacity. And in fact, researchers have discovered that parents with high IQ’s tend to have children with high IQ’s, while parents with low IQ’s tend to have children with low IQ’s.

Does that prove that intelligence is inherited, which implies that a person is a slave to his genes? The founders of the IQ industry certainly thought that this was the case. However, consider the fact that, unless a child does not learn to speak at all, the children of English parents speak English, the children of Spanish parents speak Spanish, and the children of French parents speak French. Surely the ability to speak a certain language is not inherited, but is dependent on the language that the child hears on a daily basis! In the same way, IQ and intelligence might be dependent on the child’s environment, and specifically the quality and quantity of education that he receives. Perhaps being raised in an intellectual home with intelligent parents tends to increase a child’s IQ.

Research on the role of the environment in children's intellectual development has demonstrated that a stimulating environment can dramatically increase IQ, whereas a deprived environment can lead to a decrease in IQ. A few such research studies are listed below. They confirm that IQ is all but a fixed quantity.

The Glenwood State School

A particularly interesting project on early intellectual stimulation involved twenty-five children in an orphanage. These children were seriously environmentally deprived because the orphanage was crowded and understaffed. Thirteen babies with an average age of nineteen months were transferred to the Glenwood State School for retarded adult women and each baby was put in the personal care of a woman. Skeels, who conducted the experiment, deliberately chose the most deficient of the orphans to be placed in the Glenwood School. Their average IQ was 64, while the average IQ of the twelve who stayed behind in the orphanage was 87.

In the Glenwood State School the children were placed in open, active wards with the older and relatively bright women. Their substitute mothers overwhelmed them with love and cuddling. Toys were available, they were taken on outings and they were talked to a lot. The women were taught how to stimulate the babies intellectually and how to elicit language from them.

After eighteen months, the dramatic findings were that the children who had been placed with substitute mothers, and had therefore received additional stimulation, on average showed an increase of 29 IQ points! A follow-up study was conducted two and a half years later. Eleven of the thirteen children originally transferred to the Glenwood home had been adopted and their average IQ was now 101. The two children who had not been adopted were reinstitutionalized and lost their initial gain. The control group, the twelve children who had not been transferred to Glenwood, had remained in institution wards and now had an average IQ of 66 (an average decrease of 21 points). Although the value of IQ tests is grossly exaggerated today, this astounding difference between these two groups is hard to ignore.

More telling than the increase or decrease in IQ, however, is the difference in the quality of life these two groups enjoyed. When these children reached young adulthood, another follow-up study brought the following to light: “The experimental group had become productive, functioning adults, while the control group, for the most part, had been institutionalized as mentally retarded.”

The Milwaukee Project

In the late 1960s, under the supervision of Rick Heber of the University of Wisconsin, a project was begun to study the effects of intellectual stimulation on children from deprived environments. In order to find a “deprived environment” from which to draw appropriate subjects for the study, Heber and his colleagues examined the statistics of different districts within the city of Milwaukee. One district in particular stood out. The residents of this district had the lowest median income and lowest level of education to be found in the city. This district also had the highest population density and rate of unemployment of any area of Milwaukee. There was one more statistic that really attracted Heber’s attention: Although this district contained only 3 percent of the city’s population, it accounted for 33 percent of the children in Milwaukee who had been labeled “mentally retarded”!

At the beginning of the project, Heber selected forty newborns from the depressed area of Milwaukee he had chosen. The mothers of the infants selected all had IQ’s below 80. As it turned out, all of the children in the study were black, and in many cases the fathers were absent. The forty newborns were randomly assigned, 20 to an experimental group and 20 to a control group.

Both the experimental group and the control group were tested an equal number of times throughout the project. An independent testing service was used in order to eliminate possible biases on the part of the project members. In terms of physical or medical variables, there were no observable differences between the two groups.

The experimental group entered a special program. Mothers of the experimental group children received education, vocational rehabilitation, and training in homemaking and child care. The children themselves received personalized enrichment in their home environments for the first three months of their lives, and then their training continued at a special center, five days a week, seven hours a day, until they were ready to begin first grade. The program at the center focused upon developing the language and cognitive skills of the experimental group children. The control group did not receive special education or home-based intervention and enrichment.

By the age of six all the children in the experimental group were dramatically superior to the children in the control group. This was true on all test measures, especially those dealing with language skills or problem solving. The experimental group had an IQ average of 120.7 as compared with the control group’s 87.2!

At the age of six the children left the center to attend the local school. By the time both groups were ten years old and in fifth grade, the IQ scores of the children in the experimental group had decreased to an average of 105 while the control group’s average score held steady at about 85. One possible reason for the decline is that schooling was geared for the slower students. The brighter children were not given materials suitable for their abilities and they began to fall back. Also, while the experimental children were in the special project center for the first six years they ate well, receiving three hot, balanced meals a day. Once they left the center and began to attend the local school, many reported going to classes hungry, without breakfast or a hot lunch.

Other Examples of IQ Increase

Other examples of IQ increase through early enrichment projects can be found in Israel, where children with a European Jewish heritage have an average IQ of 105 while those with a Middle Eastern Jewish heritage have an average IQ of only 85. Yet when raised on a kibbutz, children from both groups have an average IQ of 115.

In another home-based early enrichment program, conducted in Nassua County, New York, an instructor made only two half-hour visits a week for only seven months over a period of two years. He spent time showing parents participating in the program how best to teach their children at home. The children in the program had initial IQ’s in the low 90s, but by the time they went to school they averaged IQ’s of 107 or 108. In addition, they have consistently demonstrated superior ability on school achievement tests.


From the examples above, and similar cases in the literature, we contend that, a human being is not merely a slave to his genes. Human life can be compared to a game of cards. At birth, every person is dealt a hand of cards — his genetic make-up. Some receive a good hand, others a less good one. Success in any game, however, is almost always a matter of erudition. It is undeniably so that there are often certain innate qualities that will give one person an advantage over another in a specific game. However, without having learned the game and without regular and rigorous practice, nobody will ever become a champion at any game. In the same way the outcome of the game of life is not solely determined by the quality of a person's initial hand of cards, but also by the way in which he takes part in the game of life. His ability to take part in the game of life satisfactorily, perhaps even successfully, will be determined to a very large extent by the quality and quantity of education that he has enjoyed.


  • Clark, B., Growing Up Gifted (3rd ed.), (Columbus: Merrill, 1988).

  • Dworetzky, J. P., Introduction to Child Development (St. Paul: West Publishing Company, 1981).

  • Skeels, H. M., et al., “A study of environmental stimulation: An orphanage preschool project,” University of Iowa Studies in Child Welfare, 1938, vol. 15(4).

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