Beyond the binary
Society often portrays sex and gender as binary opposites; male and female; masculine and feminine. Each of these social constructs beget more social constructs, thus a male should behave like this, think like this, feel like this, look like this and be interested in this and a female should behave like this, think like this, feel like this, look like this and be interested in this. Depending on location, culture, era and class, the constructions differ somewhat. Within an individuals familiar/friendship/occupational group there exists a constructed binary gendered ideal to live up to, the perfect male and the perfect female. This taps into all kinds of insecurities, "if there is such a thing as a perfect male/female and I don’t fit that physically, emotionally in other ways is there something wrong with me?"
The binary idea of sex being male or female at birth is socially constructed as although male xy chromosomes and female xx chromosomes are the most common, 1 in 1,666 birth are not xx or xy chromosomes and the figure is less if we look at sex diversity in other ways, e.g. Androgen insensitivity syndrome. Blackless et al(2000)
Biological xy males are very diverse in body shape, hormone levels, muscle mass, body hair and height, as are biological xx females. Yet there is a pressure to conform to the ‘ideal’ male/female. This pressure can lead to people feeling insecure about their bodies. Then come the comparisons on social media or with celebrities, “why can’t my body be like that?” Added to that hormones and bodies change throughout a lifespan. Puberty is a flashpoint for insecurity and fears of not being good enough as is later in life when male and female hormones drop and become more similar. At this stage in life people can feel they are losing their masculinity or femininity. At any age illnesses affecting insecurities associated with the social construction of sex can strike, such as breast or testicular cancer.
As far as brains go there is growing evidence that there is no such thing as a male brain or a female brain rather than the neural pathways in the brain develop according to the environment, Fine (2010). Thus if we lived in a society where the teaching of physics was concentrated on females and the teaching of literature was concentrated on males there would be more female scientists and more male authors in that environment.
Transgendered people feel their body is the biologically the wrong sex. Again there is diversity, some transgendered people feel "I was assigned male/female at birth but I feel female/male", whereas other transgendered people don’t feel biologically binary.
There is the wonderful diverse spectrum of gender. Beyond the binary social constructed masculine and feminine sits any given individual, who can choose whether to take the ideas of masculinity or femininity as part of their identity or not. Sometimes this conflicts with expectations of others. Even the emotional expression can be pushed down by internalised ideas when growing up, for example, boys don’t cry or girls don’t shout.
Ultimately, we have agency over of bodies, identities, feelings, behaviour, preferences and we all have a right to choices, whether you are a masculine man who adores ballet, a trans woman wanting gender reassignment to feel you or an individual who rejects the binary man/woman s/he labels.
References
Blackless, M, Charuvastra A, Derryck A, Fausto-Sterling A, Lauzanne K, and Lee E. 2000. How sexually dimorphic are we? Review and synthesis. American Journal of Human Biology 12:151-166.
Fine, C. (2012) Delusions of Gender. London: Icon Books