the wide variety of characteristics, predominantly physical, but also behavioural, which provide indicators of one’s biological sex. Endosex individuals have sex characteristics typical of either males or females, whereas intersex individuals (that is, people with intersex variations) may have any number of sex characteristics which may not be identifiable as “typical” for males and females, or possess sex characteristics which are “typically” not all-male or all-female; that is, they may have, for example, a majority of “typical” female sex characteristics, but one or more “typical” male sex characteristics.

The use of the word “typical” or “usual” is important in this respect, because sex characteristics are based on exactly that; there are endosex individuals who may not possess a particular sex characteristic; this does not necessarily make them intersex, nor does it mean they are not men or women.

Sex characteristics are typically defined as “primary” and “secondary”, with “primary” sex characteristics being those an individual are born with, and “secondary” sex characteristics occurring during puberty. Primary sex characteristics can be further divided into relating to gonads, chromosomes, sex hormones, internal and external genitalia, and secondary sex characteristics relating to typical physical features.

Our current definitions of typical sex characteristics is based on what is immediately visible, or what has been determined through the use of medical technology (e.g. chromosomes); there could be other sex characteristics typical of men and women which are yet to be defined, and there are sex characteristics which are typical which are not essential: for example, one example of a sex characteristic typical in men is a deeper voice that develops in puberty – it does not mean a deeper voice is essential for being a man, nor that a woman who possesses a deep voice is therefore a man.

The wide variety of “typical” or usual sex characteristics which are to be considered in biological sex has began to be seen in many scientific circles as being on a spectrum, rather than on a simplistic binary, and distinct from constructs of gender, although related.