it boils down to the fact that the functional interactions within cells, though consisting individually of physical and chemical interactions, nevertheless are not directly determined by the laws of nature, in the sense that a given interaction can either occur or not occur, depending on the local circumstances. This means that both possibilities exist—occurrence and non-occurrence of any given interaction—so far as the general laws of nature are concerned.
Either possibility may be actualized, but which possibility is in fact actualized in a given instance will depend entirely on local circumstances, and not on any consideration of first principles of physics or chemistry. In other words, you cannot explain the physical interactions occurring in living things through the direct application of physical laws alone.
A concrete example that is often cited in this connection is the DNA molecule. There is no law of physics which mandates the particular arrangement of the four perpendicular nitrogenous bases, ACGT, along the sugar-phosphate backbone. On the contrary, it is precisely the fact that any of the four bases can occur in any position along the backbone, so far as the underlying laws of physics are concerned, upon which the function of the DNA molecule depends. This independence of the specific physical interactions in living systems from the general laws of physics is a deep and mysterious aspect of life, and one that absolutely distinguishes life from nonlife.
Most recently, David L. Abel [author of The First Gene] has discussed this singular property of life in greater depth and with more persuasiveness than anyone before him.(5) His way of describing the property at issue is in terms of the distinction between physical “constraints” and functional “controls.” He shows in exacting detail that the control aspect of life can never come into being as a direct result of mere physical constraints. Therefore, controls must not be identified with constraints. Rather, life uses physical constraints in order to achieve control. Controls are constraints transmuted into functions.