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In 1905, psychologists 
Alfred Binet and Théodore Simon

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designed a test for children 
who were struggling in school in France.

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Designed to determine which children
required individualized attention,

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their method formed 
the basis of the IQ test.

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Beginning in the late 19th century,

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researchers hypothesized that cognitive
abilities like verbal reasoning,

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working memory, and visual-spatial skills

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reflected an underlying 
general intelligence, or g factor.

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Simon and Binet designed a battery of 
tests to measure each of these abilities

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and combine the results 
into a single score.

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Questions were adjusted 
for each age group,

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and a child’s score reflected how they 
performed relative to others their age.

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Dividing someone’s score by their age 
and multiplying the result by 100

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yielded the intelligence quotient, or IQ.

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Today, a score of 100 represents 
the average of a sample population,

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with 68% of the population 
scoring within 15 points of 100.

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Simon and Binet thought the skills 
their test assessed

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would reflect general intelligence.

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But both then and now,

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there’s no single agreed upon 
definition of general intelligence.

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And that left the door open 
for people to use the test

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in service of their own preconceived 
assumptions about intelligence.

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What started as a way to identify 
those who needed academic help

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quickly became used to sort 
people in other ways,

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often in service of deeply flawed 
ideologies.

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One of the first large-scale 
implementations

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occurred in the United States during WWI, 
when the military used an IQ test

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to sort recruits and screen 
them for officer training.

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At that time, many people 
believed in eugenics,

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the idea that desirable 
and undesirable genetic traits

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could and should be controlled 
in humans through selective breeding.

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There were many problems 
with this line of thinking,

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among them the idea that intelligence
was not only fixed and inherited,

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but also linked to a person’s race.

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Under the influence of eugenics,

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scientists used the results 
of the military initiative

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to make erroneous claims 
that certain racial groups

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were intellectually superior to others.

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Without taking into account 
that many of the recruits tested

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were new immigrants to the United States

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who lacked formal education 
or English language exposure,

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they created an erroneous 
intelligence hierarchy of ethnic groups.

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The intersection of eugenics and IQ
testing influenced not only science,

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but policy as well.

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In 1924, the state of Virginia 
created policy

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allowing for the forced sterilization 
of people with low IQ scores—

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a decision the United States 
Supreme Court upheld.

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In Nazi Germany, the government 
authorized the murder of children

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based on low IQ.

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Following the Holocaust 
and the Civil Rights Movement,

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the discriminatory uses of IQ tests

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were challenged on both 
moral and scientific grounds.

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Scientists began to gather evidence 
of environmental impacts on IQ.

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For example, as IQ tests were periodically
recalibrated over the 20th century,

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new generations scored consistently
higher on old tests

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than each previous generation.

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This phenomenon, 
known as the Flynn Effect,

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happened much too fast to be caused 
by inherited evolutionary traits.

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Instead, the cause was likely 
environmental—

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improved education, 
better healthcare, and better nutrition.

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In the mid-twentieth century,

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psychologists also attempted 
to use IQ tests

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to evaluate things other than 
general intelligence,

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particularly schizophrenia, depression,
and other psychiatric conditions.

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These diagnoses relied in part on 
the clinical judgment of the evaluators,

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and used a subset of the tests 
used to determine IQ—

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a practice later research found does 
not yield clinically useful information.

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Today, IQ tests employ many similar
design elements and types of questions

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as the early tests,

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though we have better techniques for
identifying potential bias in the test.

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They’re no longer used to diagnose
psychiatric conditions.

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But a similarly problematic practice 
using subtest scores

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is still sometimes used to diagnose
learning disabilities,

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against the advice of many experts.

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Psychologists around the world 
still use IQ tests

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to identify intellectual disability,

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and the results can be used 
to determine

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appropriate educational support,
job training, and assisted living.

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IQ test results have been used 
to justify horrific policies

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and scientifically baseless ideologies.

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That doesn’t mean the test itself 
is worthless—

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in fact, it does a good job of measuring
the reasoning and problem-solving skills

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it sets out to.

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But that isn’t the same thing 
as measuring a person’s potential.

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Though there are many complicated
political, historical, scientific,

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and cultural issues wrapped up 
in IQ testing,

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more and more researchers 
agree on this point,

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and reject the notion that individuals
can be categorized

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by a single numerical score.