The PETA animal rights group warned that breeding between Knut and Giovanna, who was moved to Berlin from Munich last year, would carry the risk of depression amongst offspring because both bears have the same grandfather.
Frank Albrecht, zoo expert for PETA Germany, said the organisation wanted to provoke Knut fans that have pressured Berlin Zoo officials to keep the couple together by saying Knut should be castrated.
"Fans have to accept the fact that Knut just has to be castrated and then there's nothing wrong with the couple staying together," Albrecht told Reuters.
The suggestion to castrate Knut, who became famous around the world in 2006 when he was raised by a trainer after being rejected by his mother, angered fans of the three-year-old polar bear.
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Albrecht said he received many calls, including one man saying he should castrate himself first.
He added that once he explained the reasoning behind his suggestion, most people calmed down.
Zoo officials have repeatedly said that Giovanna's stay in Berlin is only temporary, and that she will return to Munich this summer.
(Editing by Paul Casciato)
