Different classes of interactions.

(A) Simple trait interactions. (B) Trait interactions cascades. (C-E) Trait interactions loops. (C) One trait affecting itself. Here, the trait in the focal individual modifies its own expression, in the same individual. (D) Two traits reciprocally affect each other: trait X influences trait Y, which feeds back to trait X. (E) Three traits involved in feedback loop to themselves via multiple interactions. Boxes represent individuals, blue squares represent phenotypic traits, purple squares represent genes. Blue arrows represent matrix Ψ, showing the direction of the influence.