Zoophilia of bestiality is partly caused by irrational speciesism and anthropocentrism. Because interspecies sex occurs in nature, and because humans "are" animals, supporters argue that zoosexual activity is not "unnatural" and is not intrinsically wrong. Research has proven that non-human animals can and do have sex for non-reproductive purposes (and for pleasure). In 2006, a Danish Animal Ethics Council report concluded that ethically performed zoosexual activity is capable of providing a positive experience for all participants, and that some non-human animals are sexually attracted to humans (for example, dolphins). Some zoophiles claim that they are not abusive towards animals: "In other
Blindness in animals called "bee purple". Other animals, such as tropical fish and birds, have more complex color vision systems than humans. There is evidence that ultraviolet light plays a part in color perception in many branches of the animal kingdom, especially for insects; however, there has not been enough evidence to prove this. It has been suggested that it is likely that pigeons are pentachromats. "Papilio" butterflies apparently have tetrachromatic color vision despite possessing six photoreceptor types. The most complex color vision system in animal kingdom has been found in stomatopods with up to 12 different spectral receptor types which are thought