<P> Gender is the range of characteristics pertaining to, and differentiating between, masculinity and femininity . Depending on the context, these characteristics may include biological sex (i.e. the state of being male, female or an intersex variation which may complicate sex assignment), sex - based social structures (including gender roles and other social roles), or gender identity . Some cultures have specific gender roles that can be considered distinct from male and female, such as the hijra (chhaka) of India and Pakistan . </P> <P> Sexologist John Money introduced the terminological distinction between biological sex and gender as a role in 1955 . Before his work, it was uncommon to use the word gender to refer to anything but grammatical categories . However, Money's meaning of the word did not become widespread until the 1970s, when feminist theory embraced the concept of a distinction between biological sex and the social construct of gender . Today the distinction is strictly followed in some contexts, especially the social sciences and documents written by the World Health Organization (WHO). </P> <P> In other contexts, including some areas of social sciences, gender includes sex or replaces it . For instance, in non-human animal research, gender is commonly used to refer to the biological sex of the animals . This change in the meaning of gender can be traced to the 1980s . In 1993, the US Food and Drug Administration (FDA) started to use gender instead of sex . Later, in 2011, the FDA reversed its position and began using sex as the biological classification and gender as "a person's self representation as male or female, or how that person is responded to by social institutions based on the individual's gender presentation ." </P>

When did they change the definition of gender