Mermaids inherited their deadly song from sirens, who were originally half-bird
The seductive singing mermaid is a medieval merger. Homer's sirens were human-headed birds, and only gradually grew fish tails in art and text. That is why French and Spanish still call a mermaid a siren. And when Columbus reported mermaids in the Caribbean, he may well have been looking at manatees.
Folklore across Europe, Latin America, Asia and Africa tells of creatures with a woman's head and torso and a fish's tail. Some traditions make them omens of storms, wrecks and drowning; others show them granting gifts or falling for humans. Mermen, their male counterparts, turn up less often in stories and sightings but appear in heraldry, and the two together are called merfolk. No evidence shows they exist beyond legend, though people still report seeing them.
The English word first appears around 1390 in Chaucer's Nun's Priest's Tale, joining mere, meaning sea, with maid. An older, now obsolete term, mermin, goes back to an Old English gloss for siren from around 725, built from words for sea and female slave. Relatives crop up across Germanic languages, from Middle High German merminne to Old Norse sjókona, sea-woman, and the Nibelungenlied features two merwomen.
Early Greeks pictured sirens as birds with human heads, and only now and then as part fish by the classical period. Through the Middle Ages the fish form won out, and the sirens' trick of luring sailors with song passed to mermaids. The oldest text giving a siren a scaly tail is the Liber Monstrorum, written between the seventh and mid-eighth centuries, which calls them sea girls whose beauty and voices entice seafarers. Some credit Germanic legend, later echoed in the Lorelei and Undine stories, for the shift, though others note similar figures well beyond Teutonic culture.
Modern culture adopted them enthusiastically. Hans Christian Andersen's The Little Mermaid of 1837 set a pattern later followed in opera, painting, comics, animation and film.
Source: Mermaid
