G and g: Two markers of a general cognitive ability, or none?

Abstract

The search for general processes that underlie intelligence in nonhumans has followed two strategies: one that concerns observing differences between nonhuman species (G), the second that concerns observing individual differences within a nonhuman species (g). This commentary takes issue with both attempts to mark a general factor: Differential responding to contextual variables compromises the search for G, and the lack of predictive validity compromises g.