For the last hundred years or so, each generation has scored higher than the previous one on IQ tests. The average IQ of populations has been rising. This is called “The Flynn Effect” and is named after James Flynn, a political philosopher and IQ researcher who helped discover the international nature of this trend.

Some people believe that the Flynn effect refutes the idea that racial IQ differences are partially caused by genetics. People making this argument often appeal to the fact that the IQ of African Americans today is equal to or higher than the IQ of White people in the past. This is true, but implies nothing about why Black people score worse than White people on IQ tests. Two groups differing genetically by X magnitude in some trait does not preclude the possibility of variation in the environment causing differences in the relevant trait of an even greater magnitude.

Consider a hypothetical garden in which two crops of corn, crop A and crop B, were planted in poor soil. Let’s suppose that corn stocks from crop A were, on average, 5 inches taller than corn stocks from crop B. Now, imagine that the bad soil of the garden was replaced with good soil and, as a result, the height of both crops increased by an average of 6 inches. Because both crop’s height increased by the same amount, the 5-inch gap between crop A and crop B remains.

What does this “Flynn Effect” in height tell us about the causes of the crop height gap? Nothing. This story is obviously fully consistent with the gap being entirely due to genes, the environment, or some combination of the two, even though crop B stocks of the “good soil generation” are taller than crop A stocks of the “poor quality soil generation”.

The same logic can be applied to individual differences: that the environment can cause large IQ differences between people over generations tells us nothing about why people within a single generation differ in IQ.

The economist Thomas Sowell does not commit the fallacious reasoning just outlined, but he does say this about the fact that Black American’s mean IQ score has risen by more than 15 points in the 20th century:

“Since the black-white difference in IQ is 15 points, this means that an even larger IQ difference has existed between different generations of the same race, making it no longer necessary to attribute IQ differences of this magnitude to genetics. In the half century between 1945 and 1995, black Americans’ raw test scores rose by the equivalent of 16 IQ points.” – Sowell (2001)

Even this seemingly conservative statement is incorrect. This is because the Flynn effect represents an increase in cognitive abilities which are different than the cognitive abilities that the races differ in.

To understand how we know this, we must first note that answering each question on an IQ test requires the mind to employ many cognitive abilities at once. For instance, a common question has people listen to a string of numbers read out loud and then has them repeat the number in the opposite order that they were heard in. To answer this question, a person must employ several abilities in order to save this information in their immediately accessible memory and reorganize the information so that they can repeat it back in reverse. This is an easy example, but even the most basic measures of pattern recognition require our minds to do multiple things in-order to produce an answer.

There are some extremely basic mental abilities, called “general intelligence” or “the G factor” which are involved in all the cognitive tasks included in IQ tests. There are other “item specific” cognitive abilities that are only needed to answer specific questions.

For instance, “general processing speed” may be part of general intelligence and may help people add numbers. However, people who can generally think equally quickly may still differ in how fast they can add.

We can measure the degree to which a given question requires general intelligence, as opposed to item specific cognitive abilities, by measuring how well scores on that question predict a person’s scores on all the other questions on an IQ test.

It has been found that there is a positive correlation between how well a question measures general intelligence and how much the races differ in it. This implies that racial IQ gaps are primarily gaps in general intelligence.

Studies have also shown that there is a negative correlation between how well a question measures general intelligence and how much that question was impacted by the Flynn effect. This suggests that the Flynn effect has consisted in a rise of item specific cognitive abilities.

Thus, the Flynn effect mostly (though perhaps not entirely) represents an increase in cognitive abilities which are different than the cognitive abilities which the races differ in.

Moreover, to the degree that both phenomena involve the same abilities, their causes are different. Researchers have determined that this is the case using the following logic: if the Flynn effect has the same causes as the Black/White IQ gap then the more a cognitive ability has been impacted by the Flynn effect the more it should differ racially.

For instance, suppose that IQ differences between the races and generations were both caused by the same nutritional deficiency. Suppose further that this nutritional deficiency has a very large impact on a person’s ability to recognize patterns but a very small impact on their vocabulary. If this is the case, then we would expect pattern recognition to differ more than vocabulary both between generations and between the races.

More generally, if the two gaps have the same cause, regardless of what that cause is, then the items which differ the most across generations should also differ the most across races.

Empirical studies have investigated this and found a negative correlation between the degree to which a cognitive ability is impacted by the Flynn effect and the degree to which it differs racially. This implies that, to the degree that the two phenomena involve the same abilities, they have different causes.

Even James Flynn, a well-known egalitarian in the race and IQ debate, has made the following statement:

“The magnitude of white/ black IQ differences on Wechsler subtests at any given time is correlated with the g loadings of the subtests; the magnitude of IQ gains over time on subtests is not usually so correlated; the causes of the two phenomena are not the same.” – Flynn 2013

In conclusion, the Flynn effect and racial intelligence differences have nothing to do with each other. Intelligence differences between races and between generations are largely gaps in different abilities, to the degree that they are gaps in the same abilities they are produced by different causes, and the existence of a large gain in intelligence over time has no a priori implications on the causes of racial intelligence differences.