Molecular biology arose from a need to explain the process of heredity.  This process was explained in terms of:

1. Changes in populations of organisms (19th Century; Charles
    Darwin and Alfred Russell Wallace).

2. Traits inherited by individual organisms (19th Century;
    Gregor Mendel).

3. Chromosomal behavior in cells (20th Century; Walter
    Sutton, Thomas Hunt Morgan, Barbara McClintock).

4.  DNA interactions within cells (20th Century; Oswald
     Avery, Barbara Hershey and others).

5.  The molecular structure of DNA (20th Century; James
     Watson and Francis Crick).