¶ _The larger any part or organ the better its equipment for carrying out the work of that organ and the more does it tend to express itself._ Nature IS an efficiency expert and doesn't give you an oversupply of anything without demanding that you use it. Jaws Becoming Smaller ¶ Our ancestors developed massive jaws as a result of constant combat. As fast as civilization decreased the necessity for combat Nature decreased the size of the average human jaw. Meaning of the Big Jaw ¶ But wherever you see a large protruding jaw you see an individual "armed and engined," as Kipling says, for some kind of fighting. The large jaw always goes with a combative nature, whether it is found on a man or a woman, a child, a pugilist or a minister. Exhibit A--The Irishman ¶ The large jaw, therefore, is seen to be both a result and a cause of certain things. As the inheritance of a fighting ancestor it is the result of millions of years of fighting in prehistoric times, and, like any other over-developed part or organ, it has an intense urge to express itself. This inherent urge is what makes the owner of that jaw "fight at the drop of the hat," and often have "a chip on his shoulder." Natural Selection ¶ Thus, because every external characteristic is the result of natural laws, and chiefly of natural selection, the vital traits of any creature can be read from his externals. Every student of biology, anatomy, anthropology, ethnology or psychology is familiar with these facts. Built to Fit ¶ Man's organism has developed, altered, improved and evolved "down through the slow revolving years" with one instinctive aim--successful reaction to its environment. Every part has been laboriously constructed to that sole end. Because of this its functions are marked as clearly upon it as those of a grain elevator, a steamship or a piano. Survival of the Fittest ¶ Nature has no accidents, she wastes no material and everything has a purpose. If you put up a good fight to live she will usually come to your rescue and give you enough of whatever is needed to tide you over. If you don't, she says you are not fit to people the earth and lets you go without a pang. Thus she weeds out all but the strong--and evolution marches on. Causes of Racial Characteristics ¶ This inherent potentiality for altering the organism to meet the demands of the environment is especially noticeable in races and is the reason for most racial differences. Differences in environment--climate, altitude and topography necessitated most of these physical differentiations which today enable us to know at a glance whether a man belongs to the white race, the yellow race, or the black race. The results of these differentiations and modifications will be told in the various chapters of this book. Types Earlier than Races