Line and drawing is an innate need for us as humans, to draw, to make marks, to explore the kinesthetic possibilities of our bodies. For example, if a people become, somehow, unable to walk, often we see them in wheel chairs, but they do not become completely sedentary, most of the time. We learn through our senses and we learn best when we're able to apply as many senses as possible to our experience.
So, with the above thought in mind, why do people feel compelled to make marks of some kind?
The famous author Joseph Conrad wrote in his short story "The Secret Sharer" that "meaning depends upon sharing." There is an intrinsic need in man to communicate, to share his feelings and thoughts. From the earliest times of markings on the walls of caves, man has felt the urge to record the world he envisions, to share in this vision his interpretation of the world and to immortalize it with physical recordings of some kind.
Art has been a form of expression for so long because often what one has to express is inexpressible in words, either because the artist has not possessed the ability to yet write, or because he could not express himself through this medium. A great form of expression, art has been compared to music, a melody which "intellect only can appreciate." Certainly, at a developed level, art transcends physical matter and is impervious to time. Art unites mankind, and it provides what John Keats called "beauty and truth," and artic critic David Piper calls
a lovely synthesis of the natural with the supernatural, the ephemeral with the eternal.
It is the nature of man to share, to communicate and record what is meaningful, and "the mark" is the medium of this communication. Sometimes art speaks more eloquently and/or succinctly than words.