For much of the 20th century, intelligence test scores steadily increased across generations, a trend known as the Flynn Effect. However, researchers say there is growing evidence that this pattern has slowed or even reversed in several countries, raising fresh questions about what may be affecting human cognitive abilities.
The research, published in the journal Intelligence, examines the so called Reverse Flynn Effect, which refers to declining scores on certain intelligence tests in some developed nations.
Scientists stress that the findings do not mean people are inherently becoming less intelligent. Instead, they suggest that changes in the environment, education and modern lifestyles may be influencing how people perform on cognitive tests.
The original Flynn Effect was observed after decades of rising IQ scores in many parts of the world. Researchers believe those gains were driven by improvements in nutrition, healthcare, education and living conditions rather than changes in human genetics.
More recently, however, studies from countries including the United States, the United Kingdom, Norway, Denmark and Finland have reported that scores on some intelligence tests have levelled off or declined, particularly among younger generations.
Researchers say there is unlikely to be a single explanation for the shift. Instead, a combination of factors may be contributing to the trend.
Among the possible reasons are changes in education systems, increased reliance on digital technology, reduced reading habits, greater exposure to online distractions and widening social and economic inequalities. Environmental factors, including pollution and poorer health in some communities, have also been suggested as possible influences.
The researchers note that intelligence tests measure specific cognitive skills such as reasoning, memory and problem solving. They do not capture the full range of human abilities, including creativity, emotional intelligence or practical knowledge.
The study also highlights that the decline has not been observed everywhere. Some countries continue to record stable or improving scores, suggesting that national policies, educational standards and living conditions may play an important role.
Researchers say more long term studies are needed to understand why these trends are emerging and whether they can be reversed. They argue that improving education, supporting healthy childhood development and reducing social inequalities could help strengthen cognitive performance in future generations.
The research has been published in the journal Intelligence.
