Fluid Intelligence has Made the Most Gains

So which kinds of intellectual performance have been pushed upward by the better environments of recent decades? Surprisingly, the steepest gains have not been found in the concrete skills that are directly taught in school, such as general knowledge, arithmetic, and vocabulary. They have been found in the abstract, fluid kinds of intelligence, the ones tapped by similarity questions (“What do an hour and a year have in common?”), analogies (“BIRD is to EGG as TREE is to what?”), and ...