Figure 5. Model for the evolution of religious beliefs.

Small fitness differences can alter the evolutionary dynamics of cultural traits. N represents the genetically transmitted religious predisposition trait and T represents the culturally transmitted belief trait. For both panels, α ₁ = 0.73, α ₂ = 0.94, b ₀ = 0.02, b ₁ = 0.3, b ₂ = 0.31, b ₃ = 0.98, c ₀ = 0, c ₁ = c ₂ = 0.5, and c ₃ = 1. A. When σ ₁ = σ ₂ = 0.12, a stable equilibrium exists on the Tn-tn edge (black square), i.e. fixation of the non-religiosity allele (n) and a polymorphism between religious belief (T) and non-belief (t), which is approached from all starting points except those on the TN-tN edge, which approach the equilibrium illustrated by the black circle. B. When σ ₁ = 0.12 and σ ₂ = 0.11, a stable polymorphism (pink square) exists such that both religious and non-religious predispositions, as well as religious belief and non-belief, coexist in the population (x ₁≈0.521, x ₂≈0.127, x ₃≈0.295, x ₄≈0.057). This polymorphism is approached from all starting points except those on the TN-tN or Tn-tn edges, which approach the equilibrium illustrated by the black circles.