Does anybody know where the catchphrase originally came from?

http://4.bp.blogspot.com/_YznWrvhs9Zw/R9yttW3EcmI/AAAAAAAAAHU/43XIxkdtRE8/S1600-R/237702h51am14e6k.gif

...in an early script, Fred was supposed to exclaim, "Yahoo!!". But Alan embellished it, and improvised, "Yabba-dabba-doo!!!". And that became a part of Fred's character, as well as a part of the theme lyrics of "Meet the Flintstones", and the song Hoagy Carmichael specially wrote for his appearance in "The Hit Songwriters" episode in 1961. To this day, "yabba-dabba-doo" is forever linked to "THE FLINTSTONES" as much as "What's up, Doc?" is to Bugs Bunny...

:tv:

Yes! Here is how Joe Barbera describes the phrases origin in the book "My Life In Toons".

"How did this momentous artifact (yabba dabba do) come to be a part of The Flinstones? Originally the script called for Fred to shout Yahoo! At a recording session, Alan Reed (the voice of Fred) turned to me and asked, "Can I say yabba dabba doo here? In a stroke of blinding genius born out of years of experience, I replied, Okay"

So it was Alan Reed, the voice actor who played Fred Flintstone, who came up with yabba dabba doo!!