“…Daly and Wilson, 1988:137-161;Kappel, 1978;Mednick et al, 1988, Table 11; Nash, 1967;Taylor, 1979;Romanucci-Ross, 1973; U.S. Department of Justice, 1979: 1891. Boys often have been found to engage in more play aggression than girls [Blurton Jones and Konner, 1973;Humphreys and Smith, 1984 and references therein;Pellegrini, 1987:29 and references therein; Whiting and Edwards, 19731, although in some studies no significant sex differences are reported [cf.…”