Biological sex is all over the news lately. Whether it's via President Trump's executive order affecting passport policy, moving trans inmates between prisons or shifting the requirements for women in sports — appeals to "the biological reality of sex" are constant. In truth, biological sex, like a lot of scientific categories, is nuanced. It's defined by multiple criteria – including chromosomal, chemical and physical factors – that can, and do, change over a person's lifetime. And it's a reality that's definitely not limited to male and female.

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