Fig. 2

a Mutation rates (in units of mutations/bp/year) required to explain the branch lengths of the Y chromosomes that are highly diverged from the human reference. The dashed lines and percentages represent the branch shortening relative to the R1b1a2a1a2b branch (or the expected length given the age for Mezmaiskaya 2). The colors indicate the branches of the tree and their corresponding mutation rate. b Percentage change in branch length as a function of the past male generation time (x-axis) compared to the branch length assuming a male generation time of 32 years, a large value within the range of the estimated male generation time in modern populations [22]. The dashed lines correspond to the change in branch length assuming a generation time of 28 or 36 years