The field of Genetics dates back to the 19th century, when Mendel first established his rules of genetic inheritance. However, it was not until the mid 20th century that scientists discovered DNA through a combination of x-ray imaging and chemical detective work. By the early 1970s, the basic principles of genetics had been well established. Henceforward, pharmaceutical companies increasingly led the march into new territory, searching DNA for a hint as to origins and cures for disease. With an existing distribution system, pharmaceutical companies knew that they could market any new discoveries.