Extended Data Fig. 2 | Twigstats optimal cutoff. a, Theoretically computed 
z-score of f4(PO,P1,PX,P2) at a single genomic locus (Supplementary Note), 
assuming PX is admixted between P1 and P2 at time 0.004 (in units of 2 Ne 
generations), e.g. corresponding to 100 generations with 2 Ne of 25,000. 
Sources split at time 0.02. b , The theoretical fold-improvement of the best 
Twigstats z-score of f 4(PO,P1,PX,P2) relative to the z-score obtained with 
regular f4-statistics. We use the same parameters as in a , but vary source split 
times to illustrate the improved power for mixtures involving more closely 
related groups. c , The optimal Twigstats cutoff time as a function of the source 
split time and the ratio between the optimal cutoff time and source split time. 
d, Comparison of z-scores computed using Twigstats to the corresponding 
theoretical values shown in a .