Estimates of key parameters of chimpanzee history.

Note: Estimates of six parameters of demographic history with 90% credible intervals from bootstrap analysis (Text S4). Estimates of absolute ages (in years) and population sizes are all based on assuming that human-chimpanzee genetic divergence occurred 7 Mya, and assume 20 years per generation. For comparison, we also present estimates of the same parameters from two previous studies of chimpanzee history [11],[12]. The fact that the previous studies jointly estimated migration rate along with the other parameters means that our credible intervals are not fully comparable with the previous studies, which had to estimate more complex models. The only credible intervals that are fully appropriate to compare are those for tECWB and NECWB, since we found that they are not substantially affected by assumptions about the central-western migration rate (Figure 2).
*To make our estimates comparable to the other studies, we multiplied all the ages and population size estimates from the Won and Hey analysis [11] by 7/6 (since they used 6 rather than 7 Mya for human-chimpanzee genetic divergence), and further multiplied population sizes by 15/20 (since they assumed 15 not 20 years per generation). We did not rescale the estimates from the Becquet and Przeworski analysis [12], since they used the same estimate of 20 years per generation as we did, and assumed a mutation rate of μ = 1.0×10−9 per base pair per year, which corresponds to a calibration date of 7 Mya for human-chimpanzee genetic divergence and 0.0128 differences between these two species per base pair.