Many years ago, our slightly eccentric wedding photographer coaxed me and my newly lawful, as well as lovely, wife to say “sex” when smiling for the camera. This works just as well as the more traditional “cheese” – try it yourself.

In those days, as now, the word sex had several meanings in the English language. The main ones, however, were meanings 1.a. and 2. in the current edition of the Oxford English Dictionary – both of which relate to the categories of male and female distinguished on the basis of reproductive functions – and meaning 4.b., in which the word is a synonym for copulation or for such terms as sexual union or sexual intercourse (not to mention more vulgar words and expressions that denote the same activity). Hence, if Adam and Eve are, as we say, having sex (perhaps after a hard day of killing snakes) it means – formally, but bluntly – that they are copulating.

But this meaning of sex is surprisingly recent. The first example in the OED is from an H.G. Wells novel published in 1900, and most of the examples are from the 1950s or later. The first use of have sex recorded by the OED is from a 1920s poem by D.H. Lawrence. If you read older books, you are likely to find expressions (sexual union and the rest) that now seem quaintly euphemistic. It appears that this modern meaning of sex was still establishing itself as recently as the early 1960s. For example, Eustace Chesser’s 1960 book Is Chastity Outmoded?, an important contribution in its day to the moral debates that led up to the sexual revolution, often places the word in inverted commas when it refers to copulation, as if Chesser views it as an emerging and slightly non-standard usage. Nonetheless, it is now, as the OED informs us, the most common general sense of the word sex.

Interestingly, when this meaning of sex became common and drove out many alternatives, usage of the word gender began to evolve in response. There is a long history of gender sometimes being used for the categories of male and female, but sex was until recently the more common and obvious word. Historically, this usage of gender was partly humorous, and its predominant meaning was as a grammatical term. To understand the touch of humour in times long past, imagine if, today, I described a female friend as being “of the lesbian persuasion”. Here, the word persuasion is being used in an understandable but slightly non-standard way for comic (though alas, not very comic) effect. It would once have been almost as odd to say of an admired friend: “She is the best of all her gender.” Come to think of it, that still sounds odd to me.

As sex has increasingly come to refer to copulation or sexual intercourse or, as we say in Australia, rooting, gender has gained ground as a more euphemistic or polite term for the biological categories of male and female. This now seems to be its most common usage, and it is driving sex out of that niche. I am, for instance, often asked to provide my “gender” on official forms, where the word sex would have been used not many years ago, and I even come across bizarre usages such as same-gender marriage or same-gender relationships.

No one doubts that language changes, or that the words used to signify concepts are arbitrary in the sense that there’s nothing more correct or natural about referring to a certain kind of four-legged critter with the word dog rather than, say, chien. If people increasingly use gender to signify a concept for which they or their elders previously used sex, they are not wrong in any larger sense. Still, it’s interesting that the increasing use through the twentieth century of plain sex to refer to copulation appears to have pushed English speakers toward something more euphemistic to denote the male and female sexes – or increasingly, the “male and female genders”. This reflects an ongoing cultural unease about the physical activity of sex, despite the fact that the sexual revolution took place more than half a century ago and even though our Western liberal democracies have supposedly moved on from Christian sexual morality.

According to Church authorities in late antiquity and medieval times, sexual desire and pleasure were inherently suspect. Sexual intercourse was viewed as a sin except between a legitimately married man and woman. Even in those cases, it was justifiable only for the purpose of procreation. Sexual pleasure was not glorified in Christian texts, and indeed “excessive” pursuit of it was denounced even when the participants were properly and legally married and keen to have children. A large domain of sexual love, desire, activity, and pleasure was marked off as sinful. We might guess that lovers did not always take this seriously, and we have plenty of historical evidence that adultery, fornication, and masturbation were popular sins in medieval Europe. Indeed, they could be topics for bawdy humour. Nonetheless, they were taken very seriously by the Church, tainted with guilt, and often punished.

Exactly why sexual love, desire, and pleasure came to be viewed in this negative light is unclear and controversial. The previous Roman civilisation imposed its own moral limits on sexual behaviour, but it could also glorify exactly what the Church authorities denounced as sin, including pleasures between husbands and wives that the Church considered improperly indulgent and excessive. Clearly enough, twenty-first-century Western societies are more like the civilisation of Rome in this respect than like medieval Christendom. Nonetheless, many people evidently feel uneasy if their language sounds too much as if they’re talking about sex in the sense of sexual intercourse.

Using the particular word gender, therefore, to refer to the biological categories of male and female is not ultimately wrong. In this case, however, linguistic change is happening under pressure of a discomfort that strikes me as anachronistic and morally unattractive. Furthermore, there’s a certain amount of confusion as gender and related terms acquire still other meanings.

Second-wave feminists used the term to signify the social practices, norms, and discourses that mould men and women, respectively, into different kinds of roles, activities, and forms of self-presentation. This was (and remains) a useful concept within feminist analysis of society, and the word gender was serviceable for the purpose. It was not confusing in itself and in context. For radical feminists, gender in this sense was something to be dismantled through consciousness raising and political activism. Less radical feminists and sympathisers might not have sought the total abolition of gender – so understood – suspecting that it might have some biological basis. But they at least wanted to reduce its social presence. The thought here was that these norms, practices, and discourses were the result of multiplier effects: they’d outrun any initial biological differences that they stemmed from in the first place, and they operated in oppressive ways. For anyone working with this concept of gender, increasing use of the word gender to refer simply to the categories of male and female causes an unwelcome complication.

In addition, we now have terms such as gender identity and gender expression, which are explicated in different ways by different theorists so I will make no effort to offer an authoritative definition. For example, gender identity sometimes seems to be a deep desire to belong to a particular sex. Sometimes it seems to be a certain deeply felt affinity for the socially constructed roles, activities, and forms of self-presentation associated with one sex or the other. I don’t propose to adjudicate whether either of these, or something else again, is the “correct” meaning of gender identity, but it is difficult to keep all this clear if we are also going to refer to the categories of male and female, which remain important in a variety of social contexts, with the word gender.

In the larger picture, we are biological and sexed beings. We belong to a species – Homo sapiens – that is, among other things, mammalian, sexually reproducing, and moderately sexually dimorphic. We are also highly intelligent animals that construct extraordinarily large and complex societies. As individuals we have complex and often surprising personalities, and we relate to our societies and to each other in fascinating ways. Nothing about our self-understanding as a biological species need contradict our sociableness or our individuality, but this is a two-edged sword: we are social and individual, but also biological. Yet some of us, some of the time, seem to find that confronting.

For my part, I resist the current tendency to replace sex, employed to denote biological categories, with gender. That’s not because it is ultimately right or wrong, but because there’s no need to reach for a euphemism – and because this particular linguistic change causes confusion that nobody needs. We can just say “sex”, and as my wedding photographer knew, every time we do so it makes us smile.

Russell Blackford is Conjoint Senior Lecturer in Philosophy at the University of Newcastle, Australia.