“That’s what you might call an evolutionary spandrel, spandrels being the supports when a domes was built that later were used as decorative elements, unrelated to their original use. You create something for one purpose and it gets used for another.”
from Saving Fish from Drowning by Amy Tan
Bonus fun fact: This quote is from a character who is terribly misstating Gould’s paradigm of spandrels. His explanation is better used for adaptation by accident.