But it seems no one has ever suggested it would play the same role in vertebrates. In mammals, melanin is contained inside vesicles called melanosomes. Larger, more numerous melanosomes make for darker skin. Mackintosh suggests melanosomes might act like lysosomes in the immune system, which engulf invading microorganisms and use enzymes to kill them. In laboratory studies, melanosomes from human skin can inhibit microoganisms, says Mackintosh.
Melanin is a sticky molecule.
The bacteria and fungi get all tangled up, and it stops them from proliferating. Also, a protein called attractin is known to regulate both melanisation and immunity in humans, suggesting a link between the two. He also points out that darker-skinned people are less likely than people with fair skin to develop serious skin diseases. During the Vietnam war, for example, American soldiers from a variety of racial backgrounds were sent into the Mekong Delta. It solves a lot of problems with these other theories.