1. Darwin, C. (1859). The Origin of Species by Means of Natural Selection. The Modern Library, New York.
2. Hoffmann, A. A. and Parsons, P. A. (1991). Evolutionary Genetics and Environmental Stress. Oxford University Press, Oxford.
3. Lamarck, J. B. (1963). Zoological Philosophy. An Exposition with Regard to the Natural History of Animals. Hafner Publishing Co. New York.