
Summary of Current Understanding of the Location of Melanosomes in Different Body Tissues and Organs and Putative Functions in Major Vertebrate Classes.
Functions of Melanin in Ancient Vertebrates
A team of palaeontologists from University College Cork (Coláiste na hOllscoile Corcaigh), Ireland have uncovered how melanin, the pigment that now gives mammals and birds the colours in their skin, fur and feathers, once had a different function in our evolutionary ancestors, but, because of one of those effects of the utilitarian 'design' process of evolution by natural selection, it was also toxic. Unless, as a creationist who believes in intelligent [sic] design, you believe toxicity was a problem deliberately created so it could be solved with a clunky work-around later.
Of course, the work debunks intelligent [sic] design creationism simply by revealing the facts, especially its latest ploy - evolution = devolution!
Melanin initially evolved as part of a mineral storage system which also played a role in immunity, and was stored in several internal organs in the bodies of early amphibians and reptiles. But it has a tendency to produce free radicles and is thus mildly toxic. The benefits of a functional, albeit primitive, immune systems outweighed the damage done, but as later animals evolved improved immune systems - given added impetus by the toxic melanin, the dynamic shifted so that the net result of melanin in the internal organs was detrimental, producing selection pressure to remove it to a place of safety - namely, outside the body in the outer layer of the skin, in hair and feathers of the evolving mammals and birds.
This in turn created selection pressure favouring colouration for camouflage, display, etc, as well as protection from harmful solar radiation, so we now have a rich diversity in hair and feather patterns in the mammals and birds.