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B. Spassky, R. C. Richmond, S. Perez-Salas, O. Pavlovsky, C. A. Mourao, A. S. Hunter, H. Hoenigsberg, Th. Dobzhansky, F. J. Ayala, Geography of the Sibling Species Related to Drosophila willistoni, and of the Semispecies of the Drosophila Paulistorum Complex, Evolution, Vol. 25, No. 1 (Mar., 1971), pp. 129-143
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Spassky et al. (1971) studied this question.
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