446 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



presence of minute air bubbles between the cells of the hair occasion- 

 ally after great nervous strain, or normally in advancing years 

 (grayness). 



The coloring substance, or substances, the exact nature and differ- 

 ences of which are still a matter of some uncertainty, occurs in the 

 shape of minute granules which, in the skin, are lodged in the deeper 

 layers of the epidermis; in the eye, infiltrate various cells of the iris; 

 and in the hair, are disseminated through most of the cells of the 

 hair shaft. The pigment, generically known as melanin, is much 

 alike in various organs of the same individual, in different individuals 

 of the same race, and in different races of man ; but there are indica- 

 tions that it may represent a complex of related forms differing by 

 slight chemical variations. 



The main function of pigmentation is a protection of the skin and 

 the eyes against those rays of the sun which would be harmful to the 

 organism ; in addition to which pigment may possibly serve also as 

 an accessory means for the elmination from the system of certain 

 substances that result from the metabolism in the cells. A complete 

 lack of pigmentation, as abnormally present in full human albinos, is 

 accompanied by weakness of the eyes as well as great irritability of 

 the skin. 



The acquisition of pigmentation in man is of ancient ancestral 

 origin. According to various indications, early man, up to at least 

 the middle of the Palaeolithic period, was brown in color, with hazel 

 to dark-brown eyes and reddish-brown to black hair. He was a 

 product of the Tropics or semitropics and could not have developed 

 there without adequate pigmentation. 



Before the middle of the glacial period this early man reached 

 western Europe, which according to many indications became the 

 cradle of his further differentiation. It was primarily from Europe 

 that he spread into other parts of the world, and it was from western 

 Europe that he eventually followed the final recession of the ice 

 northward, until he peopled what are now Denmark, northern Ger- 

 many, and the Scandinavian Peninsula. 



These regions concern us particularly in this connection. Under 

 the peculiar postglacial climatic and environmental conditions of 

 north westernmost Europe, combining in all probability considerable 

 cold, damp, and cloudiness or mists with a diminished amount of 

 light, and the effects of these conditions on man's clothing, housing, 

 and habits in general, the protective pigmentation of those who 

 lived there became to a large degree unnecessary, and as organisms 

 will not tolerate for long anything that has become useless, the 

 pigmentation of the northerners was reduced. Gradually or by mu- 

 tations man grew lighter in these lands until he came to constitute 

 a blond "race". He has lost so much pigment that his skin has 



