NOTE 22I: More precisely, we expect the number of incompatibilities to be Poisson distributed with expectation λ = 0.4, so that the chance of 0, 1, 2, ... incompatibilities is e^{–λ}, λ e^{–λ}, (λ^{2}/2)e^{–λ}, (λ^{3}/2 × 3)e^{–λ}, ... = 0.67, 0.27, 0.05, 0.007, …, with fitness reduced by 1, 0.9, 0.81, 0.73, ... with these Poisson probabilities. The average fitness calculated this way is almost the same as just setting (1 – *s*)^{λ}, though.