One modern approach to understanding intelligence is to try to understand the underlying cognitive mechanisms involved. Early conceptions of cognitive limitations were based on a limited number of items or chunks such as 7 plus or minus 2. However, more recent thinking focuses on abiding individual differences in cognitive control and the role those differences play in other complex cognitive tasks. It is clear that working memory capacity should be thought of as a construct or variable that mediates between many other variables and a wide range of cognitive tasks in which control is required or useful. In a sense, we can think of working memory capacity as both a trait and state variable. There are abiding and trait-like individual differences in working memory capacity but other variables ranging from secondary cognitive load to stereotype threat and social pressure will lead to temporary reduction in capability for cognitive control in a wide array of real-world cognition.
We are likely to soon understand the brain structures, neurotransmitters, and genetic determinants of cognitive control and the role it plays in overall intelligence.