The living state of matter.

Progress in biology has been extremely fast in the second half of the twentieth century in terms of numbers and quality of data. However less attention has been paid to the revision of existing theories on living beings structure and dynamics in development and evolution. Within this frame, the discussion on the very definition of life is lagging in the sometimes ideological debate between mechanistic and holistic views often without serious trials to integrate the overwhelming amount of new data into the different theoretical frameworks. The aim of this short review is to try to define a series of parameters specific of the living state of matter on the basis of existing evidence. The analysis starts from mathematical, physical and experimental studies on DNA constraints in nucleotide distributions and the interactions with proteins in some basic processes of life. The data discussed seem to show that short and long range correlations in DNA, particularly significant in non coding regions and increasing during evolution may have been fixed because of the need of structural landscapes complementarity for DNA-protein recognition and complex dynamics. The need for highly efficient and frequent recognition between the molecules has been extended to gene expression, protein-protein, protein-ligand complex formation and to signal transduction pointing out to the relevance of plasticity on one hand, complementarity on the other. Compartmentalisation and individuality are then taken as critical conditions favouring such processes in the hierarchical networks of all levels, from the cell to organisms, populations, ecosystems, the biosphere. Finally the specific meaning in life of useful (correlated) and disruptive noise is discussed along with the dynamics of evolutionary change in terms of homeorrhetic, plastic maintenance of flexible equilibria continuously challenged by internal and external signals.