Downward causation

Complex global patterns of behavior can often be explained by simple local interactions: for example, the complex shifting patterns of flocking birds can be generated by interactions involving only a bird and tis immediate neigbors. But can the large-scale patterns re-influence the local interactions that generated them? Is there an influence down-wards from the whole to its parts? Does the cell reorganize the biochemical processes inside it in a new way? Do psychosomatic illnesses exist?.....