Sex is real


A red deer stag in autumn mist. PHOTO/Arterra/Sven-Erik Arndt/Getty

Yes, there are just two biological sexes. No, this doesn’t mean every living thing is either one or the other

It’s uncontroversial among biologists that many species have two, distinct biological sexes. They’re distinguished by the way that they package their DNA into ‘gametes’, the sex cells that merge to make a new organism. Males produce small gametes, and females produce large gametes. Male and female gametes are very different in structure, as well as in size. This is familiar from human sperm and eggs, and the same is true in worms, flies, fish, molluscs, trees, grasses and so forth.

Different species, though, manifest the two sexes in different ways. The nematode worm Caenorhabditis elegans, a common laboratory organism, has two forms – not male and female, but male and hermaphrodite. Hermaphroditic individuals are male as larvae, when they make and store sperm. Later they become female, losing the ability to make sperm but acquiring the ability to make eggs, which they can fertilise with the stored sperm.

This biological definition of sex has been swept up into debates over the status of transgender people in society. Some philosophers and gender theorists define a ‘woman’ as a biologically female human being. Others strongly disagree. I’m addressing those who reject the very idea that there are two biological sexes. Instead, they argue, there are many biological sexes, or a continuum of biological sexes.

There’s no need to reject how biologists define the sexes to defend the view that trans women are women. When we look across the diversity of life, sex takes stranger forms than anyone has dreamt of for humans. The biological definition of sex takes all this in its stride. It does so despite the fact that there are no more than two biological sexes in any species you’re likely to have heard of. To many people, that might seem to have ‘conservative’ implications, or to fly in the face of the diversity we see in actual human beings. I will make clear why it does not.

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