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Abstract
Late Pleistocene glaciations have been ascribed a dominant role in sculpting present-day diversity and distributions of North American vertebrates. Molecular comparisons of recently diverged sister species now permit a test of this assertion. The Late Pleistocene Origins model predicts a mitochondrial DNA divergence value of less than 0.5 percent for avian sister species of Late Pleistocene origin. Instead, the average mitochondrial DNA sequence divergence for 35 such songbird species pairs is 5.1 percent, which exceeds the predicted value by a factor of 10. Molecular data suggest a relatively protracted history of speciation events among North American songbirds over the past 5 million years.
