 Many people, including many feminists, have ordinarily taken sex ascriptions to be solely a matter of biology with no social or cultural dimension. It is commonplace to think that there are only two sexes and that biological sex classifications are utterly unproblematic. By contrast, some feminists have argued that sex classifications are not unproblematic and that they are not solely a matter of biology. In order to make sense of this, it is helpful to distinguish object- and idea-construction (see Haslanger 2003b for more): social forces can be said to construct certain kinds of objects (e.g. sexed bodies or gendered individuals) and certain kinds of ideas (e.g. sex or gender concepts). First, take the object-construction of sexed bodies. Secondary sex characteristics, or the physiological and biological features commonly associated with males and females, are affected by social practices. In some societies, females’ lower social status has meant that they have been fed less and so, the lack of nutrition has had the effect of making them smaller in size (Jaggar 1983, 37). Uniformity in muscular shape, size and strength within sex categories is not caused entirely by biological factors, but depends heavily on exercise opportunities: if males and females were allowed the same exercise opportunities and equal encouragement to exercise, it is thought that bodily dimorphism would diminish (Fausto-Sterling 1993a, 218). A number of medical phenomena involving bones (like osteoporosis) have social causes directly related to expectations about gender, women’s diet and their exercise opportunities (Fausto-Sterling 2005). These examples suggest that physiological features thought to be sex-specific traits not affected by social and cultural factors are, after all, to some extent products of social conditioning. Social conditioning, then, shapes our biology.