What proof is there that Humpty Dumpty was an egg?

The rhyme does not explicitly state that the subject is an egg because it probably was originally posed as a riddle.[1] The earliest known version is in a manuscript addition to a copy of Mother Goose's Melody published in 1803, which has the modern version with a different last line: "Could not set Humpty Dumpty up again".[1] It was first published in 1811 in a version of Gammer Gurton's Garland as:

Humpty Dumpty sate [sic] on a wall,
Humpti Dumpti [sic] had a great fall;
Threescore men and threescore more,
Cannot place Humpty dumpty as he was before.[2]

According to the Oxford English Dictionary the term "humpty dumpty" referred to a drink of brandy boiled with ale in the seventeenth century.[1] The riddle probably exploited, for misdirection, the fact that "humpty dumpty" was also eighteenth-century reduplicative slang for a short and clumsy person.[3] The riddle may depend on the assumption that, whereas a clumsy person falling off a wall might not be irreparably damaged, an egg would be.[1] The rhyme is no longer posed as a riddle, since the answer is now so well known.[1] Similar riddles have been recorded by folklorists in other languages, such as "Boule Boule" in French, or "Lille Trille" in Swedish and Norwegian; though none is as widely known as Humpty Dumpty is in English.[1]