Animal sexual behaviour however, is proving to be false as, "most hormones don’t influence behaviour directly. Rather, they affect thinking and emotions in variable ways (Azar, 40)." There is much more involved in sexual behaviour in the mammalian animal than oxytocin and vasopressin can explain. It is often assumed that animals do not have sex for pleasure, or alternatively that humans, pigs, bonoboes (and perhaps dolphins and one or two more species of primates) are the only species that do. This is sometimes stated as "animals mate only for reproduction". This view is considered a misconception by some scholars. Jonathan Balcombe argues that
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