text: **qpAdm simulation.**Our simulation in Extended Data Fig. 3c uses the 
  simulation model and script provided with ref. 23, although we changed 
  this script to use the human hotspot recombination map. We simulate 
  only chromosome 1. In the original simulation model, admixing sources 
  split 1,200 generations ago, with admixture occurring 40 generations 
  ago. We additionally simulate a version in which all population split 
  times and admixture times are reduced by a factor of 5. We sample 20 
  haploid sequences per population. 
  
  We implement this function in Twigstats, which, given known assign- 
  ment of each sample to a population, identifies, at each position in 
  the genome, the population with which a sample coalesces first. Our 
  implementation takes a list of reference populations as input, such 
  that any coalescences that do not involve these reference populations 
  are ignored when traversing back in time through genealogical trees. 
  If the first coalescence involves multiple different reference popula- 
  tions, this coalescence event will be assigned to each population with 
  a weight proportional to the number of samples in each population 
  involved in that event. 