Cumulative fitness gains measured and compared with two models. Test of the two model predictions shown in Figure 3 using cumulative ln-transformed fitness gains, as explained in the text. Error bars are 95% confidence intervals. A: Cumulative gains predicted by the transitive model. B: Cumulative gains observed over the four 5,000-generation intervals. C: Cumulative gains predicted by the non-transitive model. Both the A and B confidence intervals reciprocally overlap the A and B means, indicating that the prediction of the transitive model is consistent with the independently measured cumulative gains. By contrast, neither the B nor C confidence interval includes the reciprocal mean, and thus the non-transitive model is strongly rejected by the data.