How did the expression happy as a clam come about?

There are two theories about the origin of the expression "happy as a clam."

The first theory suggests that the expression originated from the observation of clams. Clams are known to have a slow metabolism and are often found in calm and peaceful environments. This led people to believe that clams are content and happy with their lives.

The second theory traces the expression back to a 19th-century American minstrel show. In one of the performances, a character named Jim Crow sang a song that included the line "I'm as happy as a clam at high tide." The song became very popular and the expression soon entered common usage.

Regardless of its exact origin, the expression "happy as a clam" has become a widely recognized idiom used to describe someone who is feeling particularly joyful and content.