Environmental, Cultural and Behavioral Influences on IQ

What are the non-hereditary influences of the IQ of Groups?

Environmental Effects on IQ

IQ raw scores have changed over time

James R. Flynn noted that raw IQ test values in the developed world were rising through the early and mid-twentieth century, and this rise has become known as the Flynn Effect. (Raw IQ test results have been, and are, altered every few years to keep the average IQ at 100 and the spread (standard deviation) at 15.) Flynn cited this rise of raw IQ scores as proof that the environment influenced intelligence. (Source 1)

The increase in raw IQ scores, which averaged three IQ points per decade in the United States, appeared in every intelligence test, and in each of their subtests, and in every age group, but was concentrated in the part of the population with lower IQ scores. IQ was being improved by non-hereditary influences. Heredity was not the entire story.

Many recent studies indicate that the positive Flynn effect has run its course and now, in most countries including the USA, raw IQ scores are decreasing. (Source 2) A study of the Flynn Effect in Norway, using 30 years of IQ tests of military conscription (every male has to enroll), found that IQs had increased up until about 1973, and then declined substantially. By using only recruited members of the same family, the study ruled out the possibility that the positive and negative Flynn effects were caused by immigration, family size, or parents being more educated. That left changes in health, education, nutrition, and media exposure (and I would add culture) as possible causes of the Flynn effect, both positive and negative. (Source 3) Another study in Denmark, where every male must enroll in the military, found that recruits’ IQ scores increased about 2 points between 1988 and 1998, but then declined by a similar amount by 2003 (Source 4) 

A discussion of possible reasons for the Flynn Effect may be found in Wikipedia. (Source 5). These reasons mainly correspond with the factors I discuss (and provide sources for) in the following section, all of which have been widely studied.

IQ effects of pre-mature birth

In the womb effects: Being born prematurely has many pernicious effects on stature, health, and on intelligence. Even spending one week less in the womb can decrease IQ by 2 or 3 points. This may be partially caused by differences in birth weight. Very low birth weights have a widespread negative influence on health and intelligence (Source 6). However, a twin born with lower birth weight usually catches up by adulthood. (Source 7). A study in Copenhagen of children born between 1959 and 1961 found that those born under 2.5 kilograms (5.5 pounds) or over 3.5 kilograms (7.7 pounds) tested about 5 IQ points less than those in the intermediate group at ages 19, 28 and 50. (Source 8). 14% of black babies in the United States are born underweight compared to 7% of white babies and 8% of hispanic babies. However, it is an open question if lower intelligence in parents causes more low weight births. Lower intelligence has been correlated with poor diet and obesity, but the opposite is true for drug and alcohol abuse. If we take the 7% difference times the IQ difference of 5 points, we would have a less than 1% effect on the whole black population

Only a few conditions of the mother have been shown to affect the cells of the child (as measured by changes in DNA “methylation” – a chemical change in DNA that controls expression). These conditions are: malnutrition, primarily during the first week of pregnancy, exposure to toxins including drugs, alcohol, lead, and certain insecticides; smoking; depression; disease and physical abuse. (Source 9)

Nutrition effects on IQ:

Surprisingly, a starvation regime during the first years of life lowers IQs only slightly. The clearest evidence for this is the 1944 Dutch famine, followed up by military records of those born just before, during and after the famine, and tests sixty years later (The average decrease was only 1/2 IQ point for those born during the famine, but 4 points if the first ten weeks of pregnancy occurred during the famine. (Sources 10 11). 

Regularly eating breakfast has been shown to have a small effect (6 – 8 points) upon IQ in children, but it goes away when they become adults.

Caffeine consumption may possibly have a small effect on IQ. (Source 12) 

Iodine deficiency effects on IQ: 

Lack of iodine in the diet lowers IQ by 8 to 15 points, depending upon severity. There is a Chinese meta-study (Source 13) and studies in Africa, India and South Europe. It is estimated that one-third of the world’s population suffers from iodine deficiency – the purple areas in the chart from WHO global database 2004 below. Gray and black areas show iodine consumption above optimal amounts, and with some health risks. There is no data from the white area. (Source 14).

Iodine deficiency was widespread in the United States before 1924 and only slowly diminished thereafter as a greater portion of table salt became iodized. Military recruits from areas low in iodine had There is no present good data for the USA, but many international studies confirm that a complete shortage of iodine during pregnancy can lead to severe consequences in children, including greatly reduced intelligence. However, there is no rigorous data as to the effects of a mild shortage of iodine, and most likely it has little effect on the children. During pregnancy and breast feeding women need double the amount of iodine.

Lack of iodine during childhood, however, can lower IQ 15 points. (Source 15). The major sources of iodine in the American diet, other than iodized salt, have been from cow dairy products, cod and shrimp, and some beans. Some foods, like soy, califlower, broccoli and cabbage, counter the effect of iodine. The amount of iodine in people’s diets has been dropping. Many have stopped using cow’s milk, perhaps substituting soy milk. Many have stopped using iodized salt, substituting kosher salt, Himalayan salt, or sea salt, which contain little or no salt.Arguably, some of the Flynn effect and the negative Flynn effect is attributable to iodine, and now iodine shortage in pregnant women is reemerging as a problem.

Screen_Shot_2019-03-03_at_2_33_05_PM.png

Iron deficiency effects on IQ:

(Map below from Source 16)

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Iron deficiency lowers IQ in children by about 5 points (Source 17) The level of anemia in industrialized nations is 10% to 20% in young children and in pregnant women; whereas in non-industrialized countries it is 30 to 40%. 

In the USA, in 1991, 9% of toddlers and 9 – 11% of adolescent girls and women were iron deficient and about one third of these were anemic. Seven percent of older children and middle aged persons were, whereas only 1% of boys and young men were. (Source 18). Black women have almost quadruple the amount of anemia than whites. A German study of 6-12 year old children, suggest that anemia may lower IQ scores. by 12 points.

Different Diets and Obesity have little affect on IQ

 

An extensive seven-year New Zealand study published in 2009 of children of European descent (Source 19) found no significant effects from different diets, with the exception of a probable negative effect from eating margarine rather than butter, and an increase in IQ up to 3 points from eating fish. (On the other hand, the average tested IQ in different nations correlates with the amount of dietary protein.). Young childhood obesity (which continues throughout life) correlates with lower IQ, but studies suggest that this is because lower IQ individuals eat more fast foods and drink more sodas. Increasing obesity after childhood does not lower IQ. (Source 20) 

Exposure to toxins and diseases lowers intelligence:

Tropical Diseases: Widely prevalent in the tropics, malaria can in some cases directly damage the brain, (Source 21), while other tropical diseases sap energy, which might prevent concentration during IQ tests. Arguably fighting such diseases diverts personal developmental resources from the brain.

Viral Diseases — COVID: Any infection may lower IQ by 3 points; those with persistent symptoms may lose 6 points of IQ, and those admitted to intensive care may lose 9 points. Reinfection may cause an additional loss of 2 points (Source(22). Tests in England of patients who were hospitalized found it equivalent of losing 10 IQ points (Source 23).

Exposure to mercury, dioxins, DDT and PCBs are known to reduce IQ. A mother’s agricultural or industrial exposure to pesticides reduces the IQS of her children by 7 points or more. (Source 24) Much pesticide exposure in the study probably came from unwashed fruits and vegetables. Blacks and Hispanics are more likely to live downwind from chemical factories and more likely to be heavily exposed to agricultural chemicals.

Lead:  Lead exposure has been, and, unfortunately, sometimes still is, an important cause of lower intelligence and behavioral problems. Small quantities of lead in the blood have great effect. Most scientific studies have been short term, under the assumption that the effects of lead wear off after a few years, but at least one study has shown this is not the case: A homogenous New Zealand group with an average childhood blood level (at age 11) of 11 units (𝛍g/dl) found that by age 38 each additional 5 childhood units was associated with a 1.5 to 2.5 point decrease in IQ, perception and memory. (Source 25)

Most researchers have also assumed that very low levels of lead exposure don’t matter, but a recent study of young children found that even a very low exposure to lead at levels well below the USA Federal guideline of 10 millionths of a gram per dl of blood was associated with a lower IQ of about 1.4 points per each millionth more lead in the blood. (Source 26)

Lead exposures have been highest in older homes and schools with lead paint, and lead pipes. Lead remains in the soil near roads. (Source 27) These are often the poorest neighborhoods with the most African Americans. Although these correlations are highly suggestive, both the above studies state that they cannot prove causality. (It could be that less intelligent individuals earned less and were forced to live in some of the worst areas.)

Many cities, like Chicago have greatly reduced lead exposures, but the low exposures that remain are many times higher for blacks than for whites. Exposure to heavy metals and toxic chemicals is worst downwind from chemical factories, where many poor people and particularly black people live. (Source 28 ) Other cities, such as Newark, New Jersey have major lead problems, concentrated in the poorest neighborhoods.

Exposure to cigarette smoke may lower intelligence: Data from an Israeli study of military recruits (siblings) who began smoking between the ages of 18 and 21 found that the IQ of the non-smokers was about 94, and that of those who smoked a pack a day was 87. (Source 29) (A possible confounder of this result would be if less intelligent Israelis tend to smoke more. Using pre-smoking — childhood — IQ as a measure, this was found to be the case in Great Britain, but in the United States the opposite was true.)( Source 30) 

Environmental exposure to cigarette smoke at ages 6 to 16, as measured by a blood chemical resulted in reduced scores in math and reading tests as well as block design and digit span tests by 2 or 3% at low levels of exposure, but up to 10% at high levels. (Source 31)

Outdoor air pollution can be discussed in terms of cigarette equivalency. Average outdoor air pollution may equal per day in the USA nearly one-half a cigarette; in the European Union about one and one-half cigarettes, in Beijing 4 cigarettes on an average day and up to 25 on a bad day. (Source 32) The eighteen most polluted cities in the world are in China, India, Pakistan and Iran.

Indoor air pollution, according to the EPA, is generally worse than outdoor pollution, and people spend 90% of their time indoors. (Source 33)

WHO estimates (2014) that more than 4 million people in developing countries die from the use of wood, animal dung, charcoal, crop wastes and coal in inefficient indoor stoves, primarily from stroke, heart disease, obstructive pulmonary disease, pneumonia and lung cancer. (Source 34)

I know of no studies that measure the impact of outdoor and indoor air pollution on the IQ of young adults. Logically, given the equivalency with smoking, IQ could be affected by a few points.

Cultural and Behavioral Influences on IQ

Birth order effects on intelligence: While spacing of children and their sex have almost no effect on IQ, birth order matters. Early studies, with conflicting results, were all subject to problems in methodology. The one very thorough study, using every Norwegian birth between 1967 and 1998 and intelligence tests of IQ given to all men before their required military service, found that (at least for Norwegian men) birth order matters. Each subsequent child, compared to the previous one, on average had a lower score on the IQ tests of 2 or 3 IQ points. (Source 35)  However, I classify this as a behavioral influence, not an environmental one, because when the first-born child had died soon after childbirth, the second-born’s IQ was was as high as if he had been first born, and this was true of the third born if the first and second born had died.)

Alcohol consumption:

This may possibly may affect IQ; studies have been conflicting.

Physical abuse or neglect may reduce IQ: 

A number of studies show a few points reduction in IQ in children and teenagers abused or neglected, but these are correlations and to my knowledge not controlled for parental IQ. For that reason I don’t consider it proven that physical abuse or neglect affect IQ.

Training can greatly affect IQ test results: 

“Practice makes Progress,” goes the adage. Individuals can improve their performance on IQ tests with practice (and a huge industry is based upon this).

Rigorous, double blind studies are few. Evidence, however, backs the following means of raising your IQ (and SAT or ACT results) : taking practice IQ tests, boning up on vocabulary; solving many mathematical problems of the type included on the tests; and finally, for SATs and ACTs, learning the strategies for taking multiple choice tests. But these methods do not work as well for those with low IQs. A second IQ test (Source 36) improved attention, learning and memory and motor functions by about 7%, language by 4%, visuospatial functions by 3% and Executive functions by 9%. A series of successive tests did not improve language or visuospatial functions, but with three tests over three months doubled the other results. More tests showed no further improvement.

A study in Norway after a school reform that required more schooling in adolescence— on average 1/6th of a year, found that IQ was raised in 18-20 year olds by .6 points. The problem with school studies, in general is that correlations don’t prove causality. Less intelligent young people may choose less schooling. Because requirement were changed, this study can show causality.

Reading, watching television and games, musical instruments:

Exposure to media can increase vocabulary and general knowledge, and thus affect especially crystalized IQ. Certain computer and board games may help develop rapid decision making and problem solving, but there is little scientific research on the topic. Learning to play a musical instrument is proven to increase brain plasticity and increase self-discipline. One study of 6-year-olds who took piano or voice lessons for a year found a gain of 3 IQ points compared to a control group. But given that child raising techniques lose their influence by adulthood, there is presently no evidence that playing a musical instrument improves IQ test results. (Source 37 and the sources therein)

Temperament, psychology, and IQ: 

Obviously, if a person does not wish to do well on an IQ test, they won’t. If they don’t care, they will do less well than somebody who cares; if they have attention disorder, if they believe they are worthless, if they are overcome with fear or depression, or if they are brooding on neurotic or psychotic pre-occupations, they will do less well. In this respect it is noteworthy that African-American parents treat their children more negatively than do white parents, allow less exploration, and are more disciplinarian.(Source 38).

Attitudes towards learning and academic success are correlated with academic results and IQ. In any endeavor, motivation is a key. Intelligence test score gains are possible, as discussed in the previous paragraph, by preparation. 

Stereotype threat and IQ:

Stereotype threat is the name given to reduced performance on tests or on other tasks due to psychological conflict induced by social suggestion of inferiority. This includes the effects from both widespread group stereotypes, and also belief in inferiority induced by authority figures or peers using stereotypical remarks or personal degradation. Studies have shown that stereotype threat has a powerful influence on test results, academic performance, and willingness to undertake difficult tasks. For example, black students in a highly selective university answered about 40% less questions accurately on a difficult multiple-choice test, when told that the test was going to be used to judge them. The white students taking the same test at the same time actually improved their performance. (Sources 39 40). Since stereotype threat seemingly mainly applies to blacks, the question arrises as to whether the susceptibility is inherited or whether somehow it is culturally transmitted. If it stems from DNA, it will continue to affect blacks in the future. If it is culturally transmitted, or somehow environment modifies what is inherited, then it may bereduced in the future.

A study which manipulated the anxiety or self-image of test takers, found that negative emotions and positive emotions decreased logical ability, but negative emotions more so. (Source 41 and references therein.)

Time of Day and amount of sleep:

Individuals who are more alert in the morning test slightly better in the morning (by up to 6 points), and those who are more alert in the evening test slightly better in the evening. Mild sleep deprivation does not affect test results.

Exercise and meditation increase IQ:

Double-blind studies suggest that both exercise and meditation will increase mental abilities somewhat, but surprisingly I cannot find studies that quantified the IQ effect.. To the extent that excessive TV watching, game playing, texting or reading prevent exercising and mindless relaxing, they may harm IQ. African American children get less exercise, partly because they often live in neighborhoods where it is dangerous to play outdoors. Partly it may be due to higher rates of obesity. (Source 42).

Discussion:

Culture affects IQ test results, though, arguably, not native intelligence. If a culture encourages learning and test preparation, values intellectual achievement and activities, and encourages exercise IQ test results will be greater than if not. If it encourages self-doubt, emotionality and undisciplined behavior, IQ test results will be worse.

Characteristics such as emotional tendencies and diligence are heritable, typically between 33% and 50%. Also, IQ levels influence cultural habits. Thus heredity influences culture. The literature on the transmission of culture, however, also points to the teachings and examples of parents and other adults.

How do children escape the influence of dysfunctional cultures, or those that do not encourage learning? There is anecdotal evidence in the autobiographies of authors. They write that parents or grandparents provided a calm environment and, against community norms, demanded high academic performance. Exceptional schools have achieved the same result, where in effect teachers replace the role of parents (with parental backing.). 

Next page: https://iqscience.net/iq-in-adult-groups/

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