Evolution of human intelligence: The Flynn effect

Human intelligence is one of the best predictors of desirable life outcomes, showing positive associations with peoples health, income, or life satisfaction. In the general population, all cognitive abilities are positively intercorrelated. This means that individuals that perform well in one domain (e.g., mentally rotating cubes in space) typically also score high in others (e.g., answering general knowledge questions). As a consequence of this positive manifold of intelligence, most researchers assume a superordinate factor of intelligence labeled psychometric g that is rooted in the intercorrelations between subordinate intelligence domains. However, population intelligence changes between generations. In fact, for most of the 20th century, intelligence scores have been increasing worldwide, a phenomenon that has become known as the Flynn effect. These IQ gains were substantial, but were recently observed to have become less pronounced. In some countries and domains, they have apparently stagnated or even gone into a reversal. Interestingly, in most studies test score changes have been shown to be negatively associated with psychometric g, even in times of IQ gains. This seemingly paradoxical observation has exacerbated the puzzle of increasingly erratic Flynn effect patterns. One part of the answer may be related to our more profound understanding of intelligence and its measurement. Modern intelligence theories comprise typically a hierarchical organization of intelligence with multiple lower-order domains that can all be measured. Inconsistent Flynn effect patterns may therefore be due to more fine-grained changes in specific domains having become observable due to progress in intelligence measurement. But it may not only measurement level sophistication, that is causing these unexpected patterns. The way that we use our cognitive abilities may have changed. Whilst in the past, having as broad a set of cognitive skills as possible may have been ideal for success, modern environments likely promote the development of very specific cognitive abilities, thus leading to ability differentiation. For instance, nowadays we consult a dermatologist when we have a skin condition but a surgeon when we need surgery whilst hundred years ago, we might have gone to the very same physician with either ailment. This is due to the increasing master of humanity in many fields. However, in a single individual acquiring the necessary expertise that goes along with mastering a certain domain may come at the prize of having to neglect others. If we think about cognitive abilities in an analogous manner, ability differentiation may have led us to become increasingly specialized, thus leading to a weakening of the positive manifold of intelligence. In this project, we seek answers to these questions by analyzing archival data and synthesizing statistical data from over one hundred years in cooperation with scientists from Spain und the United States.