Why is a happy couple is declared man and wife? Why not man and woman, or wife and husband?
One view is that upon marriage a man retains his personhood while a woman becomes a possession. Similarly, the word mankind implies that only males are people, thus excluding half the population.
Language is fascinating. My interest in the history of the English language began in high school when my English teacher had us listen to a recording of Beowulf‘s prologue in the original Old English:
Hwæt! Wé Gárdena in géardagum
þéodcyninga þrym gefrúnon
hú ðá æþelingas ellen fremedon.
It’s hard to believe that this is actually English. But English’s Germanic origins were dramatically altered after the Norman French invasion of England in 1066. Geoffrey Chaucer wrote the Canterbury Tales in the late 1300s, six centuries after Beowulf:
Whan that Aprill, with his shoures soote
The droghte of March hath perced to the roote
English has always been a rapidly changing language, and this remains the case today. People sometimes ask when Americans lost their English accents. But reality is that Americans never had a modern British accent. English sounded very different in the early 1600s when the first settlers landed at Jamestown.
But back to the original question of sexism when declaring a couple man and wife.
Originally the phrase simply meant man and woman. The Old English word for an adult female, single or married, was wif (pronounced weef). An adult male was wer (pronounced ware). But wer eventually disappeared (the only form in Modern English is found in werewolf).
And there was a gender neutral word that meant person: mann. Being gender neutral, a female could also be called a mann. The Old English compound word wifmann meant female person, and eventually became woman. But the definition of wif, now wife, narrowed to exclude unmarried women. Wer fell out of use, however, and man became the masculine when referring to a specific person while retaining its gender neutral status when referring to people in general, such mankind.
By the late 20th century man and mankind no longer felt gender neutral and thus were seen as excluding women. And so a new gender neutral word was needed: humankind.
Because the word wife no longer means any woman, married or unmarried, many couples now choose to be pronounced husband and wife. The Old English word husbonda meant head of the household, and usually referred to a married man, though any male head of household could have claimed the name. But the term was always male.