For many centuries, Tai Chi was practiced privately, passed on from father to son in the Chen Village in northern China. (This passing of knowledge from one generation to another is known as lineage, a term which is still used to describe the transmission of a particular form from master to student.) Beginning in the mid-1800's Master Yang Lu Shan, founder of the Yang Style form, was the first to teach Tai Chi publicly. It soon became popular in martial arts circles as an advanced self-defense method. In the early 20th century Lu Shan's grandson, Master Yang Cheng Fu, promoted Tai Chi as a health exercise. Since then, it has enjoyed widespread popularity in China. Adults of all ages practice the flowing postures every day. Many older adults begin learning Tai Chi after retirement.