1. Ewens, W. J. & Feldman, M. W. in Population Genetics and Ecology (eds Karlin S. & Nevo, E.) 303–338 (Academic, New York, 1976).
2. Ewens, W. J. Theor. Pop. Biol. 3, 87–112 (1972).
3. Watterson, G. A. Genetics (in the press).
4. Gillespie, J. H. Am. Nat. 108, 145–151 (1974).
5. Gillespie, J. H. & Guess, H. Am. Nat. (in the press).