Second-wave feminists, influenced by de Beauvoir, believed that although biological differences between females and males were innate, the concepts of femininity and masculinity had been culturally constructed, with traits such as passivity and tenderness assigned to women and aggression and intelligence assigned to men. Girls, second-wave feminists said, were then socialized with toys, games, television and school into conforming to feminine values and behaviours. In her significant 1963 book "The Feminine Mystique", American feminist Betty Friedan wrote that the key to women's subjugation lay in the social construction of femininity as childlike, passive and dependent, and called for a "drastic reshaping of the cultural image of femininity."