Timescale of humpback whale evolution. (A) Species phylogeny of 28 mammals constructed from 152 orthologs and time-calibrated using MCMCtree. Branch lengths are in terms of millions of years. Node bars indicate 95% highest posterior densities of divergence times. Cetaceans are highlighted in the gray box with mean estimates of divergence times included. (B) The effective population size (N_e) changes over time. Demographic histories of two North Atlantic humpback whales estimated from the PSMC analysis, including 100 bootstrap replicates per analysis. Mutation rate used was 1.54e-9 per year and generation time used was 21.5 years.