_Skin Color Originates in the Brain

This is a shocking and surprising statement, but it is true. Pigment cells, called melanocytes, begin in the embryo as part of the brain. Then, some of them migrate to the skin. Others stay in the brain. Pigments are closely related to neurotransmitters, which the brain uses to manifest emotions, thoughts, and actions. Surprisingly, skin and brain start out in the fetus as part of the same organ, called the neural crest.

Here is an excellent explanation from BIOLOGICAL PERSPECTIVES ON HUMAN PIGMENTATION, by Ashley H. Robins. Cambridge, Cambridge Universtiy Press, 1991.

pages 5-6:
"The conflict was eventually resolved by the extensive and elegant grafting experiments of Mary Rawles in mice. She established beyond doubt that mammalian melanocytes are not part of the epidermis but originate from the NEURAL CREST (Rawles, 1953)."

Rawles, M.E. (1953). Origin of mammalian pigment cell and its role in the pigmentation of hair. In PIGMENT CELL GROWTH, ed. M. Gordon, pp. 1-15. New York: Academic Press.

"In the embryo all brain and nervous tissue ultimately develops from cells of the neural plate. The neural plate gives rise to the neural tube and, after closure of the neural tube, to a band of cells known as the neural crest. The neural crest gives rise to different types of cells, including the dorsal root ganglia of the spinal cord, the adrenal medulla and certain components of peripheral nerve fibres (Schwann cells). But, of importance to this discussion, the neural crest also generates those cells that are destined to differentiate into the melanocyte series. Prospective melanocytes, known as MELANOBLASTS, arise from the neural crest in the second month of human embryonic life and migrate to the head region along either side of the spinal cord to the skin. They enter the dermis, epidermis and hair follicle, and differentiate into melanocytes. These cells populate the dermis in increasing numbers between weeks 10 and 12 of development. From 12 to 14 weeks they usually make their first appearance in the epidermis, although epidermal melanocytes have been identified in the embryo at as early
as 8-10 weeks (Sagebiel & Odland, 1972)."

Sagebiel, R.W. & Odland, G.F. (1972). Ultrastructural identification of melanocytes in early human embryos. In PIGMENTATION: ITS GENESIS AND CONTROL, ed. V. Riley,
pp. 43-50. New York: Appleton-Century-Crofts.

"Melanin synthesis occurs from the fourth or fifth foetal month, although the first signs of it have been detected in a 10-week embryo (Sagebiel & Odland, 1972). The dermal melanocytes decrease in number during gestation and have virtually disappeared at birth with the exception of certain sites, notably the lumbosacral area of some individuals, where their presence manifests as the 'Mongolian spot'" Mongoloid babies are born with a brown spot on their backs which eventually disappears.

Pages 128-129: "Mongolian spot"
"This is an area of blue-black pigmentation, situated over the lower part of the back and the buttocks, which is present at birth (Fig. 8.5). It represents the persistence of melanocytes in the dermis, the blue colour being an optical effect due to Tyndall scattering (see p. 72). The Mongolian spot was so called because it was originally thought to occur exclusively in Mongoloid people, but although it does exist in about 95 percent of Mongoloid infants, it is also observed in a similar proportion of Negroid babies and in 75 per cent of 'Cape Coloured' newborns. Although it is occasionally seen in dark-complexioned European Caucasoids, it never occurs in blond chidren with blue eyes."
In colonial Mexico, the Mongolian spot was used to distinguish whites from Mestizos. Children with the spot were called "purple tails" and put in a lower social class. In South Africa, the presence of the spot was used to distinguish white-looking Cape Coloured from real Whites.

"In addition to the skin, melanoblasts are disseminated from the neural crest to other sites--most important of these are the uveal tract of the eye (which includes the iris but not the retina), the inner ear, mucous membranes (particularly of the mouth) and leptomeninges (membranes enveloping the brain and spinal cord). The retinal pigment layer of the eye also contains melanocytes, but these derive from the outer layer of the optic cup and not from the neural crest."