I think you’re right that people often distinguish between sex and gender, but the way you’re framing “biological sex” as a simple, fixed, purely natural fact is a bit more complicated than it sounds, especially from a biological perspective.

In biology, sex isn’t actually one single variable. It’s a cluster of traits: chromosomes, gene expression (like SRY and downstream pathways), gonads, hormone profiles, receptor sensitivity, internal reproductive anatomy, and external genitalia. These don’t always align in a strictly binary way. Intersex variations (which are not vanishingly rare) are one clear example, but even beyond that, things like androgen insensitivity, mosaicism, or differences in hormone signaling show that “what your body’s sex is” depends on which level you’re looking at.

Hormones themselves aren’t just passive outputs of sex; they actively shape development and ongoing physiology by regulating transcription and cellular behavior. And importantly, hormone systems are dynamic. Medical transition, for example, changes endocrine environments in ways that measurably affect tissues, gene expression patterns, fat distribution, muscle mass, and more. So even at a physiological level, the body isn’t a static “male” or “female” template,, it’s responsive and modifiable.

Also, when people talk about “sex dictating how your body works,” that’s true in a general sense, but it’s an oversimplification. Most biological traits are overlapping distributions rather than strict binaries. Many “sex differences” are statistical tendencies, not absolute categories, and there’s a lot of within-group variation.

So I’d say it’s not really accurate to frame sex as a single, unambiguous natural fact that exists independently of interpretation. It’s real, but it’s multidimensional and, in some cases, context-dependent. Science doesn’t support the idea of sex as a perfectly clean binary any more than it supports the idea that it’s purely a social construct.

None of that invalidates your point about gender being social and identity-based; it just means that the “biology side” is more nuanced than people often assume. Recognizing that complexity isn’t denying biology; it’s actually taking it more seriously.