Variations on the concept of the 'eternal feminine' have been invoked by thinkers as diverse as Dante, Bacon, Rousseau and Goethe to reinforce the belief in inherent differences—and a subsequent hierarchy—between men and women. Men, according to this scheme, were depicted as embodying the active, penetrative principle responsible for activities such as conquest, dominion and calculation, while women were said to represent passivity, modesty, purity, gracefulness, servility, politeness and nurturing.
Such challenges would eventually rise to new heights when French existentialist philosopher Simone de Beauvoir declared in The Second Sex that gender is not an eternal, inescapable metaphysical, or even biological, essence, as had been traditionally assumed, but merely a social construction that robs women of their freedom to determine their own destinies and identities. In what has become perhaps the most famous line in her book, Beauvoir argues: "One is not born, but rather becomes, a woman."
Femininity is not 'secreted by the ovaries,' nor is it 'enshrined in a Platonic heaven.' It is, rather, the result of a particular—and regrettable—situation according to which Man is considered as self-identity, whereas Woman is always defined as Other, as not-man. Man is the Absolute, Subject, autonomous, active, self-defined, independent, strong, positivity. Woman, on the other hand, is defined as Other, as Object, as inherently alien and alienated, as naturally constrained by her body, as negativity, passivity and reaction, as dependent and weak. This, of course, Beauvoir thinks, is absolute bullshit. :)
And if that kind of animation isn't your thing, and you'd prefer some 8-bit, 80's style video-game animation, we have that too:
Other philosophers, such as Judith Butler, have thoughtfully expanded on Simone de Beauvoir's work, making important distinctions and contributions to our understanding of the construction of gender:
And here is Butler herself on the performative aspect of gender construction:
And if you're curious to learn some more about Beauvoir's life, work, philosophy and influence, there's a really nice introduction over at the BBC's In Our Time.