An organ, serving for two purposes, may become rudimentary or utterly aborted for one, even the more important purpose, and remain perfectly efficient for the other.
Bi helburutarako den organo bat aztarna-organo edo guztiz abortatu bilaka daiteke helburuetariko baterako, agian garrantzitsuenerako, eta zeharo eraginkor iraun, berriz, bigarren helbururako.