Gender (the concept of masculinity and femininity) is a social construct.
The hierarchical structure of gender is upheld in order to maintain social control.
Gender is a social construct because its perception is fluid, and changes among time and societies.
Gender categorization only exists through the societal attribution of specific behaviors as indicating a specific gender identity, as at the individual level the internal conception of one's identity does not need labels.
Gender is determined by biological factors.
Most cultures divide labor between men and women, thus at least some aspects of gender are universally shared and not socially constructed.
Men and women as well as masculine and feminine naturally complement each other. They evolved to be this way and to be attracted to the opposite sex.
According to three main monotheistic religions' scriptures, God created the man and the woman as different and complementary.