Human intelligence is on the decline, according to the Huffington Post, writing about a recent study suggesting that westerners have lost 14 I.Q. points since the Victorian Era. Study co-author, Dr. Jan te Nijenhuis, professor of work and organizational psychology at the University of Amsterdam, says that because women of higher intelligence tend to have fewer children than do women of lower intelligence, intelligence is being selected out of the affluent populations of the west.
|The Kallikak family, promoted by eugenicist Henry Godard as proof of heritability of idiocy|
The problem is that this study and all others pointing to a causal relationship between birthrates and IQ are seriously flawed. Indeed, even the claim that IQs are declining is suspect.
Let’s start with the fact that the IQ test, developed by Alfred Binet, in France, wasn’t even created until 1903, two years after Victoria’s death, making it exceedingly difficult, if not impossible, to make a valid comparison of Victorian and modern Westerners’ IQs. Furthermore, the original test emphasized memorization, vocabulary and questions about appropriate behavior, none of which has much to do with intelligence. Even modern versions of the test contain some of these types of questions. IQ tests also tend to have a class bias, as well as cultural and linguistic biases (e.g., questions about appropriate behavior depend on one’s cultural background).
To address this problem, te Nijenhuis used proxies for intelligence (comparing a variety of different tests for which data does exist going back to 1884). However, he chose a very weak proxy, reaction time, which he presumed was an accurate proxy for intelligence since reaction time reflects a person's mental processing speed. However, it is not necessarily true that a person who has a quick visual reaction rate also has a quick mental processing rate for math, puzzles or other types of problem solving.
Another problem with the research is that it lacked valid controls, drawing into question the validity of the comparisons. Supposedly the Victorian and modern experiments used a similar test for reaction times, but they used different instruments for measuring the results. Thus, the average late 19th century reaction time of 194 milliseconds might have actually been much closer to or even slower than the average 2004 reaction time of 275 milliseconds had researchers used the same equipment and methods.
Bad Science in Service to Race and Class Prejudice
The researchers also used data collected by Francis Galton (Darwin’s cousin), who coined the term eugenics, which included the idea that poor people were poor due to their inferior intelligence, which they presumed was due to their “bad” genes, and that the affluent were wealthy due to their good genes. This pseudoscience was used to justify government interventions promoting or limiting birthrates among different races and social classes, forced sterilizations in many countries, including the U.S., infanticide, and genocide, as practiced by the Nazis. Thus, Galton had a significant bias going into his research, specifically an Experimenter’s Bias (i.e., observing what you expect, rather than what actually occurs). In Galton’s case, he would be expecting white and affluent people (who also had smaller families) to be smarter, and could have inadvertently designed tests that would have given him these results.
|Image from Wikipedia, based on Galton's Ideas|
Te Nijenhuis’s research suffers from some of these same problems, particularly the presumption that intelligence is essentially a heritable trait (i.e., passed through the DNA), a presumption still shared by a large number of scientists as well as the lay public, despite a lack of credible data to support this idea (more on this below). However, his race and class prejudices also come out in his belief that “high-IQ people are more productive and more creative,” and his nostalgia for the flourishing of creativity and brilliance of the Victorian era. He uses the term dysgenics in his work, a term that is often associated with the eugenics movement thanks to the work of Richard Lynn, who argued in his book Dysgenics: Genetic Deterioration in Modern Populations, 1996, that human genetic health was declining because criminals have higher birthrates than the rest of the population (there is no evidence they have higher birthrates and it is unlikely that criminality is heritable), leading many, including Lynn, himself, to renew calls for eugenic policies.
|Many states had similar sterilization laws, resulting in 10,000s of forced and voluntary sterilizations in the 20th century|
Genetics is Not Destiny
While large numbers of scientists and the lay public believe that intelligence is highly heritable, there is no conclusive evidence for this. Indeed, estimates of the heritability of IQ range from as low as 40% to as high 90%, suggesting that intelligence is at least partly, and possibly quite significantly, influenced by factors other than DNA. Part of the reason why there is so much controversy over the degree to which intelligence is heritable is that no genes for intelligence have been positively identified, (though recent research has located positions on certain chromosomes where some genes related to intelligence might be located).
Intelligence and IQ, like most phenotypes (traits), are influenced not only by DNA, but by environmental influences and sometimes even by random events that occur during development. ABO blood type, for example, is 100% heritable, meaning that it is determined entirely by the DNA inherited from the parents and no environmental factors influence it. Human height is around 94% heritable. However, even a relatively high heritability of 94% is not sufficient to presume a cause and effect relationship between DNA and a particular phenotype. A person with tall parents could easily wind up being short if he does not have access to a diet rich in protein and calcium. Indeed, when one considers stereotypically short ethnic groups, most come from regions of the world with high levels of malnutrition in which protein and calcium are relatively scarce. Similarly, average human heights in Western Europe and the U.S. have increased 4” over the past 150 years, according to Scientific American, most likely because of improvements in childhood nutrition that occurred during that period.
There are many environmental factors that influence learning, memory, and even reaction time. Memory and reaction time, for example, can be improved with certain exercises and practice. Exposure to high levels of stress can impair memory and learning due to overexposure to the stress hormone cortisol (see here, here and here). How parents communicate with infants and children can influence the size and depth of their vocabularies (see here and here), which can influence how they comprehend phenomena and their ability to solve problems. Malnutrition and hunger can lead to cognitive impairment (see here, here and here).
Another problem with te Nijenhuis’ findings is that low IQ parents, while they may have larger families, do not necessarily produce low IQ children (“Resolving the debate over birth order, family size, and intelligence,” Rodgers, Joseph Lee; Cleveland, H. Harrington; van den Oord, Edwin; Rowe, David C. American Psychologist, Vol 55(6), Jun 2000, 599-612).
Confusing Correlation With Causation
Despite the fact that te Nijenhuis is a scientist, he apparently has difficulty distinguish between correlation and causation. There is considerable evidence that populations with higher IQs have lower birthrates. Thus, I.Q. and birthrates have a negative correlation (i.e., as one goes up, the other declines). However, this does is not evidence that one is caused by the other. Rather, they could both be products of one or more other causes or the correlation could simply be a coincidence.
Social class also correlates with both birthrate and intelligence. Wealthier women tend to have fewer babies. There are several logical explanations for this such as delaying motherhood to pursue college and career, for affluent women, versus having children earlier and more often among poor women because children can help with the farm work and care for you in your old age.
Wealthier people, in general, also tend to have higher IQs. However, this may have far more to do with environmental and social factors (e.g., access to better nutrition and healthcare, better quality schools, being read to more often as babies and toddlers, less stress, greater access to enriching extracurricular activities, like travel abroad, summer school and camps) than genetics. Indeed, two studies done in Texas and Minnesota seem to support this. According to the studies, the correlation in intelligence between mothers and biological children were not only quite low (0.20 to 0.34, respectively), but not much different than the correlations between mothers and adopted children (0.22 to 0.29, respectively), suggesting that social and environmental factors likely had a greater influence on children’s intelligence than the genetics of their mothers (Richard Lewontin, Not In Our Genes). In other words, intelligent people may very well be intelligent more as a consequence of their social class privileges than their parents’ genes.