To put the matter graphically, it may be said that our body wears two tight-fitting physiological coats, called the epidermis or overskin, and the cutis or underskin.

The overskin is not simple, but consists of an outside layer of horny cells, such as are removed by the razor on shaving, and an inside mucous layer, as seen on the lips, which have no horny covering.

The underskin contains nerves, fat cells, hairbulbs, and numerous blood-vessels, some as fine as a hair, all embedded in a soft, elastic network of connective tissue.

The overskin has none of these blood-vessels; but as it is very delicate and transparent, it allows the colour of the blood to be seen as through a veil. In the extremely blond races of the North nothing but the blood can be seen through this veil; but in the coloured races the lower or mucous layer of the overskin contains a number of black, brown, or yellowish pigment cells. The colours of these cells blend with that of the blood, thus producing, according to their number and depth of coloration, the brunette, black, yellow, or red complexion. The palm of the negro’s hand is whiter than the rest of his body, because there the horny epidermis is so thick that the black pigmentary matter cannot be seen through it. And the reason why every negro is born to blush unseen is because the pigmentary matter in his skin is so deep and abundant that it neutralises the colour of the blood.

Now, why do the races of various countries differ so greatly in the colour of their skin? This is the most vexed and difficult question in anthropology, on which there are almost as many opinions as writers.

The oldest and most obvious theory is that the sun is responsible for dark complexions. Are not those parts of our body which are constantly exposed to sunlight—the hands, face, and neck—darker than the rest of the body? and does not this colour become darker still if we spend a few weeks in the country or make a trip across the Atlantic? Do we not find in Europe, as we pass from the sunny South to the cloudy North, that complexion, hair, and eyes grow gradually lighter? And not only are the Spaniards and Italians darker than the Germans, but the South Germans are darker than the North Germans, and the Swedes and Norwegians lighter still than the Prussians.

The same holds true not only of South America as compared to North America, but of the southern United States compared to the northern. It also holds true of the East, where, as Waitz tells us, “The Chinese from Peking to Canton show every shade from a light to a dark-copper colour, while in the Arabians, from the desert down to Yemen, we find every gradation from olive colour to black.” Moreover, aristocratic ladies in Japan and China are almost or quite white, whereas the labouring classes, as with us, are of a darker tint.

These and numerous similar facts, taken in connection with the circumstance that the blackest of all races lives in the hottest continent, and that Jews may be found of all colours according to the country they inhabit, lead almost irresistibly to the conclusion that it is the sun who paints the complexion dark.

Nevertheless there are numerous and striking exceptions to the rule that the warmer the climate the darker the complexion. To obviate this difficulty, Heusinger in 1829, Jarrold in 1838, and others after them, have endeavoured to show that the moisture and altitude, as well as the direct action of the sun, had to be taken into consideration. But since “D’Orbigny in South America, and Livingstone in Africa, arrived at diametrically opposite conclusions with respect to dampness and dryness,” Darwin excogitated the theory (which, he subsequently found, had already been advanced in 1813 by Dr. Wells), that inasmuch as “the colour of the skin and hair is sometimes correlated in a surprising manner with a complete immunity from the action of certain vegetable poisons, and from the attacks of parasites ... negroes and other dark races might have acquired their dark tints by the darker individuals escaping from the deadly influence of the miasma of their native countries, during a long series of generations.”

The testimony on this point being, however, conflicting and unsatisfactory, Darwin gave up this notion too, and fell back on the theory that differences in complexion are due to differences in taste, and were created through the agency of Sexual Selection. “We know,” he says, “from the many facts already given that the colour of the skin is regarded by the men of all races as a highly important element in their beauty; so that it is a character which would be likely to have been modified through selection, as has occurred in innumerable instances with the lower animals. It seems at first sight a monstrous supposition that the jet-blackness of the negro should have been gained through sexual selection; but this view is supported by various analogies, and we know that negroes admire their own colour.”