The Concepts of Complexity and Emergence

There has evolved over the past three decades a set of general concepts that have revolutionized the way we regard and study systems in nature. Their basic premises run counter to the Newtonian reductionistic approaches and might thus be labelled post-Newtonian concepts. The central theme of this new philosophy is the recognition that the behaviour and properties of a system are non-linear combinations of the subsystems. Such a system is endowed with complexity and displays specific properties that emerge from dynamic interactions between the subsystems. We discuss briefly complexity and emergence as the two pillars of post-Newtonian thought. 

We define emergent properties of a system as those that are possessed by the system itself in its globality, but are neither properties of the components nor linearily derivable from them. Emergent properties arise from the interactions between the constituents of a system, when these transactions are of such a nature and magnitude that the individuality of the parts is subsumed in an unrecognizable form within the larger system. In other words, emergent properties are seen in systems whose component parts interact with such intricacy that they cannot be predicted by standard linear equations. 

Closer to home, and as discussed in detail later, we can cite the properties of a molecule as being emergent and not predictable from a linear combination of atomic properties. The identity of the individual atoms in a molecule is lost in the extensive electronic interactions that occur when a molecule is formed. The physical properties of the atoms are no longer of significant value in understanding the molecule. Other steps must be taken if we are to achieve some understanding. 

Emergence, in other words the existence of emergent properties, is the specific characteristic of, and the necessary condition for, systems said to display complexity. Emergent properties and complexity are thus two manifestations of the same phenomenon and have come to be recognized as characteristics of nature at every level. But whether emergent properties are also the sufficient condition for complexity remains to be clarified. 

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The concepts of complexity and emergent properties, discussed here within the context of drug research, must become integral parts of every step in this collective effort as it is practised today and as it evolves to newer methods tomorrow. However, and this remark is so important that it was kept for the end, these new concepts are not meant to replace the traditional mechanistic approaches that have proven so successful in drug research. Rather, the post-Newtonian vision must blend with the Newtonian philosophy to enlarge and enrich our mental world. As so aptly stated by Edward O. Wilson, the father of sociobiology (quoted in Lewin, 1993) ... 

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