Results of coalescent simulations comparing gene versus population histories. Distributions of expected values of the test statistic, s, derived from 500 coalescent simulations over a variety of demographic histories. A: Eight populations originating from a common ancestral population representing a fragmentation model (inset). B: Seven populations structured by a matrix of distances from the CVA of calls, representing an isolation by (call) distance model (first letter of population indicates position on tree). Observed discord between gene tree and population tree is indicated with an arrow.