In the end

In the end contemporary art is just the newest genre of art. It may use different techniques, materials, and have a different goals. However the subjects aren't anything new, artists' works have depicted the same types of subject matter for centuries. People have been drawing maps since man first observed that the world wasn't uniform. Spiritual or religious imagery is the oldest known form of art, originating in cave paintings. Artists have been fascinated by the human body since time immemorial.

If the themes are nothing new then what is it that sets Contemporary Art apart from any older work?

Contemporary Art is unique in the materials and techniques involved. Spiritual images are the oldest form of art yet no previous era would have thought to convey them a stuffed cotton stag with worsted viscera pouring. The body has fascinated artists for millenia yet no previous era would have strapped machine parts to their body and called it art, or creating a synthetic ear for that matter. However the greatest change that contemporary art has introduced is the idea of process art. the idea that the act of making a work could be the art and not what was made. No previous era would have ever considered random pencil marks on a wall brilliant art because the man made them while chained to the floor; or black streak on the floor art because a woman painted them with her hair. Contemporary art's real innovation is process art, for it is the most unique and original concept.