This section is from the "The New Student's Reference Work Volume 5: How And Why Stories" by Elinor Atkinson.
" To tan " has two meanings. One is to turn anything a yellowish-brown color. The other meaning is to toughen and harden skins into leather. In the making of leather, both the toughening and the coloring are results of the processes of tanning. So it seems to be in the case of exposure of our skins to a great deal of hot sunshine. When a city child, who has lived in the house and in shaded streets, goes on a vacation to a farm or the seashore in mid-summer, the first effect of the exposure to sun rays is burning of the tender skin. This would not do at all, for burned skin blisters and peels. Different things in our bodies always rush to any injured parts to heal and protect them. A dark surface absorbs heat better than a light one. So to protect the skin from the heat, a dark pigment or paint is formed by blood cells and sunbeams acting together. This not only darkens the skin but toughens it, too. Our skins are really "tanned" something like leather. Do you see why brown and black people are natives of hot countries where there is much sunshine, while the fairest nations of the white race live in cold, northern countries where there is the least sunlight?