The idea of the model organism first took root in the middle of the 19th century with the work of men like Charles Darwin and Gregor Mendel and their respective work on natural selection and the genetics of heredity. These early works in finding standards to compare organisms against continued into the 20th century as the first model organisms were brought into laboratories. Beginning in the early 1900s Drosophila entered the research laboratories and opened up the doors for other model organisms like Tobacco mosaic virus, E. coli, C57BL/6 (lab mice), etc.