General intelligence : myth or reality ?

The notion of general intelligence arises from the observation that performance across a large array of cognitive tests is correlated, such that a factor analysis yields one factor explaining a substantial part of the variance. This statistical observation has led Spearman (1904) to postulate that a single biological or psychological property ("g" for general intelligence) underlies the performance in all intelligence tests and subtests. Although this hypothesis has been debated for a whole century, it has become widely accepted, both within intelligence research and in related fields. For instance, it underlies brain imaging studies on "the neural basis of intelligence" as well as (largely unsuccessful) attempts to find genes associated with general intelligence. Yet it has become increasingly clear in recent years that there is no such thing as general intelligenceroscience.