How to Analyze People on Sight
Constant repetition of the same kinds of thoughts or emotions finally makes permanent changes in that part of the body which is physiologically related to these mental processes.
The Evolution of the Jaw
¶ The jaw is a good illustration of this alliance between the mind and the body. Its muscles and bones are so closely allied to the pugnacity instinct center in the brain that the slightest thought of combat causes the jaw muscles to stiffen. Let the thought of any actual physical encounter go through your mind and your jaw bone will automatically move upward and outward.
After a lifetime of combat, whether by fists or words, the jaw sets permanently a little more upward and outward--a little more like that of the bulldog. It keeps to this combative mold, "because," says Mother Nature, the great efficiency expert, "if you are going to call on me constantly to stiffen that jaw I'll fix it so it will stay that way and save myself the trouble."