Gender is a Spectrum

There are two terms that we use more or less interchangeably - sex & gender - but which actually mean slightly different things (depending on who you ask). 

As I see it, sex usually refers to someone's biological sex (as characterized by the genitalia and other secondary sex characteristics you were (or weren't) born with, or by the chromosomes you were or weren't born with), whereas gender is the outward expression of one's sex - how you think of yourself/label yourself or how you are thought of/labeled by outsiders who interpret your behaviors (how you dress, how you wear your hair, your mannerisms, your ways of speaking, how you process or express emotion, how you interact with others, etc.) through the lens of contemporary gender stereotypes.

Often (but not always), one's sex and one's gender are the same - such as when a biological female considers herself to be a woman, and embraces/identifies with many (but rarely all) stereotypical behaviors of contemporary womanhood. These people are cisgender, also known as "gender-straight" or "gender-normative," meaning they conform to the gender/sex based expectations of society. 

Other times, a person's self-concept of gender does not match the sex they were assigned at birth. These individuals might identify as transgender. They may reject the stereotypes of the sex they were assigned at birth in favor of ones that better match their self-concept, may dislike the parts of their biology that do not represent the gender they feel they truly belong to, and may request that those they interact with change the gender pronoun they use to refer to them. They may take hormone treatments or go through surgeries to transform the parts of their biology they dislike, so that their physical appearance better matches their true gender. Some individuals who are transgender know from a young age that there is a disconnect between their minds and bodies; others do not realize it until much later in life. It is best not to assume any of these things, because every transgendered individual (just like every person in general) is unique and experiences life differently. 

>> Side note #1: Rejecting some gender roles does not automatically change someone's gender - "effeminate" men and "tomboyish" women exist, and they are not less of a man or less of a woman than manly men or feminine women (unless they want to be). 

>> Side note #2: A person's gender identity is not the same as their sexual orientation. Though being attracted to women is a stereotypical gender characteristic for many men, it is only one of many. Someone could be a gay man (and therefore reject one of the stereotypes of their male gender role), or even an effeminate gay man (and therefore reject many of the stereotypes of their male gender role), but still identify as male. Similarly, a woman could be attracted to women, or even be attracted to women and reject other female gender stereotypes, but still identify as female.

Behaviors or proclivities are gender-specific only because we have made them so. Women are not inherently "more nurturing" or "more domestic" than men. All genders/sexes are capable of providing quality childcare, and in completing household chores; like any other tasks, these are tasks that one gets better at with training or practice. Behaviors that we see associated with women, and behaviors we see associated with men, are things that women and men do because of how they are brought up, what they are taught, how they are treated, and social norms they are exposed to and encouraged to emulate (whether consciously or subconsciously).

Gender characteristics are fluid, changing throughout time and differing among cultures. For example, in America, it used to be acceptable for all children, regardless of gender, to wear dresses, and the color pink used to be associated with boys and blue with girls. In another example, some cultures associate displays of emotion as exuding manliness, while others associate emotional sensitivity with femininity. It doesn't take too much research to realize how arbitrary those characteristics are assigned to one gender or another - and not too much further thinking, once one has reached that realization, to conclude that it is ridiculous to insist that women or men "should" act a certain way. There is more than one way to be a man; there is more than one way to be a woman.

Gender is therefore more of a spectrum than a simple binary between male and female. You can have supposedly masculine traits even if you're a woman; you can have supposedly feminine traits even if you're a man. In recent years, this has developed into some people choosing to identify as neither a man nor a woman, or choosing to identify as both man and woman. They are the same person they always were; they are merely looking for a more appropriate label to use for themselves - a label that recognizes the arbitrariness of gender characteristics/the lack of a gender binary, and a label that encompasses how they truly feel about themselves and what group(s) they belong to, or want to belong to, or want not to belong to.

Some terms you may hear include:

• agender: a person who is internally ungendered or who does not have a felt sense of gender identity
• bigender: a person whose gender identity is a combination of a man and a woman
• pangender: a person whose gender identity is comprised of all or many gender expressions
• gender diverse or gender non-conforming: a person who either by nature or by choice does not conform to gender-based society expectations
• gender fluid: a person whose gender identity or presentation shifts 
• genderqueer or gender non-binary: a person whose gender identity is neither man nor woman, is between or beyond genders, or is some combination of genders; often used as a reaction to/commentary on the social construction of gender, gender stereotypes, and the gender binary system

Sex characteristics seem more rigid at first glance (males have penises; females have vaginas), but are actually just as fluid as cultural gender conventions. There are different ways to define one's biological sex, and all of them are less clear-cut than the strict male-female binary we suppose. 

You could define sex by observable, external characteristics (penises and scrota and facial hair, vulvae and hip width and breast size), or by internal sex organs (ovaries, uteri, prostrates) - but to use such a narrow definition would be to exclude or shame those who have had hysterectomies or mastectomies or other surgeries, those whose secondary sex characteristics are inconsistent with their primary sex characteristics (i.e. a "bearded lady" or someone with "man boobs"), and those who were born with conflicting or absent characteristics (i.e. an intersex child born with male and female organs, or a child born without any reproductive organs at all).

A male does not stop being male just because he's had surgery on his prostrate. A large-chested female is not "more female" than a small-chested female. Nor does a starving female who starts to grow extra body hair (to keep her skeletal frame warm) or lose the ability to menstruate (due to a lack of key nutrients in her diet) stop being female because of these physical changes to her body.

Every body is different; these differences can occur naturally, from genetics or environmental factors (such as diet), or they can occur medically, due to life-saving surgeries, medications, or elective procedures. They could even occur through abuse, such as someone who has had their genitals mutilated or altered. Girls who have had their vulvae stitched shut are still girls, just as the man whose wife famously cut off his penis is still a man.

How then can we insist there is a standard body that every male should have, or a standard that every female should have? Every female body looks different from every other female body, every male body looks different from every male body, and there are still other bodies that do not fit cleanly into a male or female category at all.

You could also try to use hormones to divide humans into males and females, looking at levels of testosterone, progesterone, or estrogen. But some males or females have naturally occurring levels of hormones that are typically found in someone of another sex, and others see altered hormone levels due to medical treatments, surgeries, or medication side effects. 

Females with Type 2 diabetes, for instance, have pancreases that must produce extra of the insulin hormone - and sometimes increased production of other hormones, as well, including testosterone, which can affect ovulation and fertility. PCOS (polycystic ovary syndrome) is another common illness which can affect hormone levels and impact reproductivity. 

Should such individuals no longer be considered female, just because of hormone imbalances or fertility difficulties? Of course not! If being female only meant that one was capable of ovulation, then girls could not be considered female before menarche either, nor older women after menopause. As much as it sometimes seems like we're heading in that troubling direction, we are emphatically not living in Margaret Atwood's The Handmaid's Tale; females are worth more than their ability (or willingness) to bear young.

Finally, you could also classify people by chromosomes - XX for female, and XY for male. But there are other chromosome combinations that naturally occur in humans, including Turner syndrome (X0, or only one sex chromosome), Triple-X syndrome (XXX, or even XXXX or XXXXX, where multiple X chromosomes are inherited), Klinefelter syndrome (XXY or XXXY, where extra X chromosomes are inherited with a male Y chromosome), and XYY (aka Jacobs) syndrome. 

Some of these individuals see their fertility compromised because of their condition; others see no obvious symptoms that they have a chromosomal abnormality and go through their entire lives never knowing. 

People who are born with any of the non-typical XX or XY chromosome combinations listed above, and/or people whose reproductive or sexual anatomy at birth does not seem to fit the typical definitions of female or male are known as intersex. These individuals are proof that gender is a social construct; there are not "only" two sexes, and therefore not only two genders, either. Sex/gender is a spectrum, rather than a simple either/or. Whether you look at physical characteristics, hormone levels, or chromosomes, there is more variation than the dichotomous "female" and "male" categories we are taught.

And so, if sex and gender are divided rather arbitrarily into different categories, than it makes no logical sense to treat people differently or give people different privileges or limitations based on their sex or gender. This is what feminism is - an insistence that woman and men should have equal rights and equal opportunities. Women and men should earn equal pay for equal work, should be treated with the same dignity and respect, and should feel valued and safe in whatever realm of society they choose to inhabit. 

"Woman" and "man"; "female" and "male" - these are just words, just labels that we came up with in an attempt to understand our world. Their definitions can change, just like any word evolving over time. Furthermore, new words can be added to the lexicon if needed (and I would argue - they are needed). There should not be any controversy in this - it is just people trying to explain their experience, use words carefully and conscientiously, and have some say in how people are or aren't labeled. There is no harm to it, and in fact often a great deal of good. Discovering who you are and who you want to be, and being allowed to define yourself as you see fit, are important aspects of being human and being free.