Alexander, R. D. et al.1979 In: Evolutionary Biology and Human Social Behavior (Chagnon, N. A.& W. Irons (eds.)). pp. 402-435. Duxbury Press, North Scituate.
Boinski, S.1987 Behav. Ecol. Sociobiol.21: 13-21.
Cheverud, J. M. et al.1985 Evolution 39: 1335-1351.
Clutton-Brock, T. H. et al.1977 Nature 269: 797-800.
Crook, J. R.1972 In: Sexual Selection and the Descent of Man (Campbell, B.(ed.)). pp. 231-281. Aldine, Chicago.