The existence of this more and more important issue of the difference between Gender and Sex is one of the most obvious proofs that Language is what defines our reality. The existence of the two terms is not only controversial but what is more, they do not exist in each and every language. Most languages do not distinguish between biological and social sexual identity.
Yet in English, Gender is usually considered to be a socially constructed form of identity, while sex is biologically determined.
Related: Engendering of subjectivity
It is of crucial importance for the political discourse that we have to understand that both Gender and Sex are words, before all else. The notion that the sexual identities of humans are nothing more than a social construct is an obvious mistake on the part of those who assume that is possible.
For example, in the animal Kingdom, especially in the mammalian species, both sexes have specifics of both behaviour and sexual selection. As the animals do not have consciousness, nor do they have societal norms (conscious societal norms that is), it is impossible for their roles to be socially constructed. Therefore, the sexes do have specific roles and proclivities.
That said, it is possible for people to artificially distort the natural roles of one or both sexes. Still, that is not to say that it is one of the sexes who represses the other, nor that the fact that boys prefer to play with cars, and girls with dolls, is something that “society” have made them prefer.
Numerous researches from all over the world including (and especially) the Scandinavian countries have shown that the more the people in charge try to “lower the differences” between the sexes, the bigger the manifested differences will be, once they grow up. Men will still prefer to play with “things” (e.g., computers, cars, phones, electronics, tools), while women increasingly prefer to work with other people (being nurses, for example).
Related: Consciousness