Natural selection doesn't explain systematicity
Evolutionary theory alone isn't sufficient to explain systematicity, as it doesn’t describe its constitutive bases. It can describe the historical origins of constitutive bases, but only after the constitutive bases themselves have been described.
Brian McLaughlin, 1993b.
Constitutive Bases: Capacities to work together to constitute a higher-order capacity. For example, the capacities to have the beliefs that "John loves Sally" and "Sally loves John" are both constitutive bases of the higher-order capacity to have systematically related beliefs about John, Sally, and love.