A couple of times, I’ve received a facebook message passing on the information that the phrase “blood is thicker than water” derives from an older expression “The blood of the convenant is thicker than the water of the womb”, suggesting that the original meaning was basically opposed in sense to the modern meaning.
I can find any number of disreputable references to this idea on the electric intarweb, e.g.:
This notion has the certain ring of bullshit, and I can’t find any serious scholarly reference backing it up.
The Font Of All Wisdom mentions:
The equivalent proverb in German (originally: Blut ist dicker als Wasser), first appeared in the medieval German beast epic Reinhart Fuchs (c. 1180 ‘Reynard the Fox’) by Heinrich der Glîchezære, whose words in English read, ‘Kin-blood is not spoilt by water.’
By 1670, the modern version was included in John Ray’s collected ‘Proverbs,’ and later appeared in Sir Walter Scott’s novel ‘Guy Mannering’ (1815) “Weel — Blud’s thicker than water — she’s welcome to the cheeses." and in English reformer Thomas Hughes’s ‘Tom Brown’s School Days’ (1857).
This WP article also mentions that Jewish congregational leader R. Richard Pustelniak and British humorist author Albert Jack have published the idea of the “blood of the convenant is thicker than the water of the womb” origin.
It all adds up to a thumbs down, in my book, but I would be interested in hearing your thoughts.