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.
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| 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.
 |
| Alfred Binet |
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.
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| 1920s pseudoscientific image trying to connect brain types to criminality |
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.
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| 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.
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| 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.
