The Price equation (George Price, 1970) decomposes evolutionary change into selection and transmission (mutation/drift):
where z is a trait (here: fitness itself), wᵢ is individual fitness, w̄ is mean fitness. The covariance term = selection; the expectation term = transmission bias (mutation, development). Fisher's Fundamental Theorem follows: Δw̄ = Var(wᵢ)/w̄ when transmission is faithful. Multilevel selection (kin/group selection) arises from Price equation's recursive hierarchy. The simulation tracks a trait distribution under a Gaussian fitness landscape: selection sharpens the peak, mutation spreads it, drift perturbs small populations. The covariance term (blue) and transmission term (orange) are shown live — watch them balance at mutation-selection equilibrium.