So, what is sex? Most of us are taught that there are only two biological sexes, male and female. Shortly after your first breath, a doctor most likely examined you and assigned you one of those two sexes. However, for intersex people, also referred to as people with differences of sexual development, the categories of male and female don’t necessarily fit. In considering people with differences of sexual development, researchers have argued that there are as many as five to seven common biological sexes and that sex actually exists along a continuum with many different variations. Estimates suggest that as much as 1.7 percent of the population has some variation of sexual differentiation. It’s much more common than you might think! But, how do we qualify sex? Again, it’s a tricky subject that even scientists can’t seem to quite agree on. Is your sex determined by your genitals? By your chromosomes? By your predominant sex hormones? Is it a combination of the three? For folks with differences of sexual development, genitals, chromosomes, and predominant sex hormones can vary from what is considered “normal” for males or females. For example, people with Kleinfelter Syndrome are often assigned male at birth, but have XXY chromosomes and may have low testosterone levels and other physical variations such as wide hips and enlarged chest tissue. Indeed, intersex folks have distinct needs for which the categories of male and female simply aren’t useful. Transgender people, or folks who were assigned a sex at birth that doesn’t align with their gender identity, also call into question the category of biological sex. For those transgender people who have chosen to pursue physical transition by taking hormone replacement therapy to make testosterone or estrogen their predominant hormone, by having chest or genital confirmation surgery, or both, these markers of biological sex again may not line up as we’ve been taught to expect.