In the 1940s, biologist Alfred Kinsey embarked on a series of experiments that would revolutionize the way we perceive human sexuality (and earn a posthumous portrayal by Liam Neeson in “Kinsey”). The most lasting aspect of his legacy is the Kinsey scale. It posited that human sexuality could be described on a scale ranging from zero (exclusively heterosexual) to six (exclusively homosexual), with shades of both in between. This scale would set the stage for the modern notion that sexuality is fluid, and that the categories of "gay," "straight," and "bi" are hopelessly reductive.

But our notion of gender―which is distinct from, though linked to, sexuality―did not have a Kinsey figure to fight for it, and so many people's conception of gender remains rooted in a binary of "male" and "female." If you are not one, you are the other. And if you are neither, you are distinctly other.

The reality is a little more complicated, says Nicole Avallone, interim deputy director of programs and policy at the LGBT Community Center in New York. "Every single person experiences and expresses their gender in a way that is unique and their own," she says. "In this expansive idea of gender identity and gender expression, gender can no longer be just two things, male or female."

So, what is the gender spectrum?

To understand the gender spectrum, it's necessary to distinguish between the terms "sex" and "gender," which, like gender and sexuality, are related, but not interchangeable. Sex is biological, the set of reproductive parts you are born with. Gender is more a function of identity: Your perception of yourself as male, female, or other, and the way you choose to present yourself to the world as male, female, or other. This may or may not match your biological sex.

Instead of the male-female binary, think of gender as a continuum, says Avallone. "In our society, expressing your gender in a certain way―say, wearing pants and wearing your hair short ―is often associated with a certain line, being either closer to that box of 'male' or that box of 'female.' But if we're seeing gender as a continuum, each person might place their location along this continuum slightly differently."

Cass Liebman, a health and wellness intern at the Brooklyn Community Pride Center, "lives in the center of two genders," for instance. Liebman, who identifies as genderqueer (neither exclusively male, female, or trans), uses the preferred gender pronoun (PGP) "they."

"It was very difficult for me to use 'they' as a singular pronoun at first, because I could hear all of my grammar teachers screaming in my head. But that is the closest thing I have that feels correct."

"What my genitalia is has nothing to do with my gender identity," Liebman explains. "It has to do with the way that I understand and represent my own personal cocktail of masculinity and femininity." The notion of the gender spectrum, then, like the Kinsey scale, holds that there are many places between "male" and "female" that a person can occupy. And these places are fluid and may change over time, or even day-to-day.

Consider gender privilege

People who are cisgender -- meaning their biological sex matches their perceived gender identity -- benefit from privilege in subtle ways. Consider how simple it is for a person who is biologically female and who identifies as such to use a public restroom marked "women." Or the ease with which a person who is male in both biology and gender identity can check a box marked "male" on a government document or a form at the doctor's office. These are episodes that can be psychologically challenging, even damaging, for a person who falls somewhere outside of these boxes―to say nothing of the overt violence and hostility that can be directed at people who visibly fall outside the norm.

And a person who falls outside the norm―who has likely always fallen outside the norm―may have been shamed for having a non-standard gender identity (a girl who hates pink, a boy who plays with dolls) from a young age. "So often, people's gender expression is shut down very early on because of this locked-in concept that this child was assigned male, or this child was assigned female, and therefore these are the ways that child is allowed to be in the world," Avallone says. "It is really destructive to a person's sense of themselves. People start suppressing and hiding really core parts of who they are and what feels good to them about who they are."

The language barrier

Part of the difficulty of conceptualizing gender as something more than simply male and female stems from language itself. We like things to be neat, concrete, and easily labeled by language. But that can make it tricky to wrap one's mind around something that falls outside of language. In many cases, the LGBTQ community has had to adapt vocabulary -- vocabulary that tends toward the black and white -- to cover a spectrum of sexual and gender identities that bleed into other shades. This can breed misunderstanding. How does one use a term like "queer" or "transgender" when it seems to mean something slightly different to every person who uses it?

"Any time someone identifies as something other than male or female, we want to give them another box to fit in―like ‘trans’―because we're more comfortable with that," says Avallone. "You're either this or you're that, or you're something else. But when you do that, you still risk assigning certain expectations that you've created or that you've been told of what transgender is. Some people may say, 'I don't fit inside any one box.'"

Unlike "transgender," which refers specifically to a person's gender identity (broadly speaking, "trans" can apply to anyone whose gender identity does not align with their biological sex), "queer" is more of an umbrella term that captures many aspects of both gender and sexuality―a signifier that signifies many things at once, resisting easy categorizations.

"'Queer' is this overarching term, which is part of the reason I use it. It confuses people, and that makes me happy," says Liebman. "Essentially, if you equate 'queer' to a spectrum, you're in the right ballpark."

How can you can be more gender-inclusive?

Be aware.

Simply being aware that a person's gender can fall outside of a binary is a good first step. As recognizing that if you identify as a if you identify as a cisgendered person, you may be benefiting from gender privilege, Avallone explains.

"I challenge people to spend just one day where they pay attention to every single time gender comes up. That can be walking into a public bathroom, or hearing people say gendered things like, 'Boys don't cry,' or, 'Don't be a sissy,' or walking past a hair salon and seeing a sign that says 'men's cuts' and 'women's cuts.' What might it be like for a person whose gender doesn't match that binary? How many points of potential discomfort does that person have to live with every single day?"

Check your language.

While you're at it, purge your own vocabulary of gendered phrases like, "Real men are…," or "Real women have…," says Liebman.

"If I wake up one day and say, 'I'm a man,' that's what a real man is. Even saying something like, 'A real woman has curves,' can be shaming to those who fall outside of that narrow definition. Some women are naturally skinny and beautiful. Some women are curvy and gorgeous. Some women are mega fat babes. And that's a wonderful thing."

Use the right pronoun.

Yes, it can be difficult to get accustomed to referring to a single person as "they"―or "ze," or "ve," for that matter―but it's a sign of respect to adapt a person’s preferences. And if you do mess up, which is natural, "Correct yourself and move on," says Liebman. "Normalize, normalize, normalize. The one thing you should absolutely not do is go, 'Oh my god, I'm so sorry, I'm so, so, so, so sorry.' Because then you're just attracting more attention to it. "

Ask questions.

If you're not sure what pronoun a person prefers, ask. "As long as it's gently―'I heard you refer to yourself as this, is that what you prefer?'―it's better than continuing to make a mistake over and over again," Liebman says. "Some people may not feel comfortable talking about it. If they say they don't want to talk about it, then let it go."

Use your head.

There are limits to what's appropriate to ask, and common sense should be enough to tell you when you've crossed a line. "If you're going up to someone and saying, 'Have you had surgery? Are you going to start testosterone?' you're basically saying, 'I need to know what your genitalia is, because not knowing makes me uncomfortable,'" says Liebman. "You would never ask these questions of someone who was cisgender. 'Hey, what's your penis like? I have questions.'"

Here are some questions you should stay away from asking:

For more information and resources, check out genderspectrum.org.