Increasing fluid intelligence is possible after all

Abstract

Almost 40 years ago, Jensen (1) claimed that, when all is said and done, there is not much one can do to raise people's IQs. Over the years, there have been various attempts to do so, which generally have yielded somewhat ambiguous results (2). Even successful attempts (3) have typically involved training people on the same kinds of items on which they would be tested, so that it was not clear whether the training was generalizable, rather than merely a result of practice effects on particular item types (4). Further complicating the picture have been studies showing that IQ tends to be fairly highly heritable, with most reliable estimates ranging from ≈0.5 to 0.8 (5). More recently, heritability has been found to vary both with age, with IQ becoming more highly heritable in later years (6), and with social class, with IQ more highly heritable in higher social classes (7). Although heritability does not imply the fixedness of a trait (e.g., height is highly heritable but also modifiable), the mixed results of training studies have been taken to be consistent with the notion that IQ is relatively fixed. IQ may be viewed as a composite comprising multiple elements: In many theories of intelligence, a distinction is made between fluid and crystallized intelligence (8). Fluid intelligence comprises the set of abilities involved in coping with novel environments and especially in abstract reasoning; crystallized intelligence is the product of the application of these processes. Fluid intelligence is often measured by tests such as figural analogy, classification, and matrix problems, whereas crystallized intelligence is measured by tests of vocabulary and general information (9). In this issue of PNAS, … *E-mail: robert.sternberg{at}tufts.edu