The rare name Yarnell had only appeared in the U.S. baby name data a couple of times (as a boy name) before suddenly being given to dozens of babies — of both genders — in 1977:
| Boys named Yarnell | Girls named Yarnell | |
| 1980 | . | 9 |
| 1979 | 6 | 6 |
| 1978 | 17 | 22 |
| 1977 | 25 | 41* |
| 1976 | . | . |
Why?
The spike can be traced back to mime team Shields and Yarnell, made up of married couple Robert Shields and Lorene Yarnell. Their TV variety show, The Shields and Yarnell Show, debuted in 1977 (but was canceled in 1978).
If you don’t remember the show, perhaps you remember their robots having breakfast routine (video). It was one of the skits they performed on a 1979 episode of The Muppet Show.
P.S. There was no equivalent spike for the name Shields, in case you were wondering.
P.P.S. The original appearance of Yarnell in the data in 1962 (as a boy name) can be attributed to TV actor Bruce Yarnell, who was appearing in the TV Western Outlaws at that time.