Despite a strong condemnation from some conservative Christians, the Oslo Natural History Museum has put on display several pieces of art that show homosexuality among animals. The exhibition entitled "Against Nature" is claimed to be the world's first on one of the most controversial subjects.

"Homosexuality has been observed for more than 1,500 animal species, and is well documented for 500 of them," Geir Soeli, the project leader of the exhibition told Reuters in an interview.

The museum stresses that with well established evidences over the presence of gay or lesbian behaviors among giraffes, penguins, parrots, beetles, whales and dozens of other creatures, homosexuality in humans should not be considered "unnatural."

"The sexual urge is strong in all animals. ... It's a part of life," Soeli said.

One of the exhibits at the museum shows a photograph of two giant erect penises flailing above the water as two male right whales rub together. Another shows a male giraffe mounting another for sex and another describes homosexuality among beetles and birds.

Soeli pointed out that Bonobos, a type of chimpanzee, are among extremes in having sex with either males or females, apparently as part of social bonding. The subject of homosexuality among animals has often been ignored by researchers, partly due to lack of interest and partly due to fear or ridicule from the conservative society.

Citing a study by Italian researchers, Soeli said that it were the genes which determine homosexuality in men and women.

"The same genes that give homosexuality in men could give higher fertility among women," he said.