Words change over time in order to reflect the culture where the language is spoken. The whole purpose of words is to differentiate shades of meaning so that we can communicate information to other humans as precisely as possible; as the needs of a language’s speakers change, the words they use will need to change and adapt, too. Languages have been changing and adapting since, oh, forever actually. The language you are reading now descended from the same common ancestral language, Proto-Indo-European, from which most of the other languages spoken in Europe descended, excluding a few such as Finnish, Hungarian, Estonian, and the freakiest of all languages, Basque.
Why aren’t we all still speaking Proto-Indo-European? There are a number of reasons, but one reason is because different groups of speakers living in different places will need to talk about different things and draw different semantic distinctions. Because of this (and other reasons), languages are always evolving and changing.
One part of language that changes is its lexicon. For instance, if you read Laura Ingalls Wilders’ series of books about pioneer life, you will see the word “store boughten” or “boughten” used, as in Almanzo received a boughten cap for Christmas. It was unusual to buy such items in a store back then, since everyone made them at home, but nowadays buying things in the store is the normal way to acquire them, so we would never call such things “boughten”. Instead, we want to differentiate things that are made at home, since that is now the exception. Therefore, I might wear a homemade dress, and you might eat homemade jam. The language adapted with the culture; the word boughten has fallen out of use and the word homemade has taken its place.
So it is with the words sex and gender. The word sex used to be used to refer to the male and female of a species and the word gender was used to refer to grammatical markers on nouns, articles, and adjectives. If you are in your Russian 101 class, you need to use the word gender when referring to the fact that stol (table) is grammatically masculine and sobaka (dog) is grammatically feminine.
But when else would you need to use the word gender to talk about grammar? Um, never actually. We don’t have gendered grammatical declension in English, so it isn’t something we need to talk about outside of the second language classroom.
In our grandparents’ day, the word sex was perfectly unambiguous for talking about the male and female of a species. If you used the word sex, everyone knew that’s what you meant, and no one would be confused about whether or not you were actually talking about sexual intercourse. It wasn’t ambiguous because up until the sexual revolution, people didn’t talk about sexual intercourse (or any other kind of sexual activity) outside of their doctors’ offices or their Anatomy and Physiology classes. Since they spent so little time in those places, there was no imminent need to make a distinction about which kind of sex you meant.
But now we talk about sexuality all the time. It’s common in our culture, and if you say the word sex to someone on the street and ask them to define it, I would bet that the vast majority of people will immediately think about the sexual meaning of the word and not the male/female meaning of the word. We talk a lot about sexuality but very little about grammar, so where we really need to draw our linguistic distinction in order to give semantic precision is between sexuality and maleness/femaleness, not between grammar and maleness/femaleness. The most expedient way to do this is to stop using the word sex to refer both to sexuality and to the male and female of a species and instead use sex only to refer to sexuality. The word gender can then be used to refer to the male and female of a species and for the most part no one will be confused because how likely is it that you are talking about foreign language grammar?
Here’s the wikipedia version of how gender came to be used to refer to the male and female of a species:
Sexologist John Money introduced the terminological distinction between biological sex and gender as a role in 1955. Before his work, it was uncommon to use the word “gender” to refer to anything but grammatical categories. However, Money’s meaning of the word did not become widespread until the 1970s, when feminist theory embraced the distinction between biological sex and the social construct of gender. Today, the distinction is strictly followed in some contexts, especially the social sciences and documents written by the World Health Organization (WHO). However, in most other contexts, even in some areas of social sciences, the meaning of gender has undergone a usage shift to include “sex” or even to replace the latter word. Although this gradual change in the meaning of gender can be traced to the 1980s, a small acceleration of the process in the scientific literature was observed when the Food and Drug Administration started to use “gender” instead of “sex” in 1993. “Gender” is now commonly used even to refer to the physiology of non-human animals, without any implication of social gender roles.
OK, so it looks like there was some kind of socio-political agenda behind this change, given that sexologists and feminists had a hand in it. Yet I don’t think they have done anything wrong linguistically (they have, however, done almost everything else wrong). The sexual revolution changed what we talk about, for better or worse, and our language has merely evolved to reflect that. We might consider whether all this sexy talk is a good thing or not, but it would be silly to cling to an old linguistic convention that obscures rather than clarifies meaning for modern speakers.
Yet sometimes people will insist that everyone must use the word gender only to talk about grammar, even though we rarely need to do so, and the word sex to talk about both sexuality and the male and female of a species. What may be happening there is that some people are looking for an easy way to mark high-status group identification: We here know ever so much more than those proles who use the word gender to refer to the males and females of a species! This reminds me of a retired English professor I worked with when I taught at a community college; he insisted upon using the subjunctive form of be, as in “If you be men of great learning…” I always wondered why he stopped at the use of the subjunctive and didn’t just go whole hog and use ye instead of you. Really, he was probably just trying to make sure everyone understood that he was a real professor with a PhD and the rest of the adjunct faculty, with our lowly Masters’ degrees, couldn’t be expected to understand complicated stuff like outdated syntactic rules.
The next time someone scolds you for using the word gender to mean the male or female of a species, ask them how well they speak Proto-Indo-European. If they are a little rusty in it and give you some excuse about not having used it much since college or that they can still read it but can’t speak it, then tell them you are going to use the word that has evolved to differentiate your intended meaning properly in modern English.
And on a final note, it is definitely the case that PC-speech has led to some clear linguistic absurdities. I have observed feminists saying things like, “All the various genders…” This is quite stupid; there are only two genders (where gender refers to the male and female of a species; in grammar there are three genders), so the correct phrase is “Both genders”. Everything other than male or female is a genetic anomaly and can be referred to by the appropriate syndromal name. So, dear reader, if you have an example of silly feminist linguistic shenanigans that serve no useful purpose (unlike the gender/sex semantic evolution), feel free to leave it in the comments for group entertainment.
Edit: Both Novaseeker and Kristor write that they are using sex instead of gender not as an act of class snobbery but rather as an act of socio-cultural linguistic activism. Novaseeker writes:
…the common parlance has changed but it wasn’t “evolution” but rather “engineering”. It was engineered top-down. And done so for very obvious political reasons. Buying into the terminology simply reinforces the distinction between biological sex and social gender — which is precisely the point of the adoption of the new term, to drive a wedge between what is given at birth and what you socially are. It’s the way the game is played.
I don’t use the word gender other than when referring to language (which is not common, but not as uncommon as it is for some others, perhaps, due to my job) not as a status marker, but as an act of resistance against this attempt to reengineer language for socio-political purposes.
And Kristor agrees:
…PC linguistic usages are a kind of jizya…When we abjure them and cleave to traditional usages, we commit acts of sedition against Leviathan.
Kristor: PC is Jizya