...reductionism will never be able to account for the role of historical contingency and accident. Even if an all-powerful being could account for all biological scenarios emerging from an initial state of the universe, it could never tell us why one particular scenario is preferred over others...evolutionary accidents by definition cannot be predicted from starting conditions because they depend on chance and opportunity. 

In addition function can never be uniquely derived from reductionism even if structure is. For instance in his book "Reinventing the Sacred", the complexity theorist Stuart Kauffman makes a powerful argument that even if one could derive the structure of the human heart from string theory in principle, string theory would never tell us that its most important function is to pump blood. The function of biological organs arose as an adaptive consequence of the countless unpredictable constraints that molded them during evolution. In addition the evolution of both structure and function was a mix-and-match process that depended as much on chance encounters as on strict adaptation. All this can never be captured in a reductionist worldview.

Why biology (and chemistry) is not physics - Ashutosh (Ash) Jogalekar, Fieldofscience.com