Sexes are a system of categories, a way of putting kinds of bodies into categories. Living things of many species evolved to be specialized into their own male, female, and intersex kinds, each known as a sex. A sex is generally determined by reproductive body parts. In humans, these imply-- but do not prove-- a correlation with chromosomes. In gender studies, the sex and gender of a person are thought of as two distinct things: sex is about the body, whereas gender is about the self.
Distinction between sex and gender
The distinction between sex and gender differentiates a person's biological sex (the anatomy of an individual's reproductive system, and secondary sex characteristics) from that person's gender, which can refer to either social roles based on the sex of the person (gender role) or personal identification of one's own gender based on an internal awareness (gender identity). In this model, the idea of a "biological gender" is an oxymoron: the biological aspects are not gender-related, and the gender-related aspects are not biological. In some circumstances, an individual's assigned sex and gender do not align, and the person may be transgender. In other cases, an individual may have biological sex characteristics that complicate sex assignment, and the person may be intersex.
The sex and gender distinction is not universal. In ordinary English, sex and gender are often used interchangeably. Some dictionaries and academic disciplines give them different definitions while others do not. Some languages, such as German or Finnish, have no separate words for sex and gender, and the distinction has to be made through context. On occasion, using the English word gender is appropriate.
Sex assignment at birth
When people speak of a person's "sex", usually what they really mean is their assigned gender at birth. This is because a person's sex is much more difficult to determine than most people believe. For example, chromosomes are part of defining someone's sex, but most people never get their chromosomes tested. A baby's assigned gender at birth is based on only one thing: the presence or absence of what a doctor thinks is probably a penis. This will be the only basis of that child's legal gender. As the person grows up, the doctor's guess about their sex can turn out to be wrong, because some intersex conditions only become clear once a person has gone through puberty. Even then, the person might have unusual chromosomes or internal reproductive organs without ever knowing about it.
See main article: intersex.
Intersex people are people born with any variation in sex characteristics including chromosomes, gonads, sex hormones, or genitals that do not fit the typical definitions of male or female bodies.
Because intersexuality is about the kind of body that someone is born with, not how they identify, intersex is not a gender, and is not the same thing as nonbinary. However, some intersex people can consider their gender identity to simply be "intersex."
An intersex person may have any gender identity. An intersex person doesn't necessarily identify as intersex, and may instead prefer to be called a man or woman. Or an intersex person may agree with their assigned gender; in this case, they would be described as either ipsogender or cisgender. Intersex people may think of themselves as cisgender, transgender, genderqueer, nonbinary, etc. An intersex person who feels that their intersex status has influenced their gender identity may identify as intergender. Some intersex people think of their intersex status as belonging to the broader range of LGBT identities.
People who identify as nonbinary aren't necessarily intersex, and instead may be dyadic (meaning not intersex).
Discrimination against intersex people
"Dyadism" is a common kind of sexism. As a concept, dyadism is the incorrect belief that humans are strictly dyadic, having only two sexes. In action, dyadism is discrimination against intersex people. That discrimination can include erasure, harassment, medical malpractice, lack of marriage rights, religious intolerance, human rights violations, and hate crimes against intersex people. Dyadism is also the basis of other forms of sexism, including binarism, the belief that people have only two genders.
Because of dyadism, doctors think of intersex conditions as an irregularity. As a result, intersex people were given so-called "normalizing" or "corrective" surgeries, often at a very young age, and without their consent.
There is some controversy around the usage of the term "dyadic." Dyad means two, so dyadic promotes the idea of a dualism for sex: male and female. Although well intended, it may fall short of deconstructing binary of sex and acknowledging the complexity of human biology.
Sexes of nonhuman animals
One common misconception is that all animals have only male and female sexes. However, nature is much more complex and varied. Many animal species are known to have a variety of intersex conditions, or very different kinds of sexes than occur among humans. For example: male seahorses that get pregnant, fish that change sex if there aren't enough of a particular sex in their group, female deer with antlers, lionesses with manes, lizards that lay fertile eggs after two females mate together (parthenogenesis), hyenas that give birth through an organ that is nearly indistinguishable from a penis, and so on. Most animals don't have sex chromosomes that are the same as the XX or XY set that are most common in humans. Learning about the diversity of animal sexes can help one recognize how much the sexes are an idea constructed by humans to describe and simplify reality, but our understanding of that reality tends to be limited by our own sexual stereotypes widespread in our culture.
To learn more about the diversity of animal sexes, read Joan Roughgarden's book, Evolution’s Rainbow: Diversity, Gender, and Sexuality in Nature and People (2009).
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