William Harvey (1640), a 17th Century anatomist, demonstrated the physical link between structure and function in the human body.
 
 
 
 


Matthias Schleiden (left) and Theodor Schwann (right) separately proposed that plants and animals were composed of individual units called cells, and that these cells were combined to form tissues, organs,
                  and organ systems.
 
 

Rudolf Virchow would further cement the concept of the cell theory by proposing that all cells arise from other cells.  This would eventually link the concept of biogenesis with heredity, since the living cell must, if it is to give rise to others like it, carry some immutable substance which guarantees its ability to do so.
 
 

In the 1930s, Linus Pauling demonstrated the physical laws which govern the arrangement of atoms within molecules when he proposed the structure of the protein molecule.  At the same time, J. Desmond Bernal began the use of X-ray crystallography to examine protein structure.  Later, Pauling, Rosalind Franklin and others would utilize this technique in their studies which attempted to describe the shape of the DNA molecule.