Addy Pross leading the discussion 'Darwinian Evolution: Essential or Contingent?'

The 'Why Life?' workshop that was held at ELSI in late January asked the life question in a way I hadn't heard asked before. Some 70 years ago Erwin Schrödinger famously asked 'What is life?', but asking 'Why life?' takes the question a step further. Could the laws of physics and chemistry actually anticipate the existence of an organizational form of matter expressing life's properties? Inspection of the physical world (of which we are a part) immediately reveals that material organization can manifest itself in those two distinctly different forms, living and non-living. But why two organizational forms, not one, or three? Why does life exist at all? Well, till recently the answers seemed way out of reach, but thanks to a new area of chemistry, termed systems chemistry, I believe our ability to deal with these profound questions is changing.

Part of the problem in addressing fundamental life questions lies in the fact that conceptually speaking the biological and physical sciences remain far apart. An 'autonomy of biology' philosophy that took hold of 20th century biology further widened the divide. However this new area of systems chemistry is beginning to bridge that gap and that is good news for biological understanding.

From a chemical perspective, biology is the study of highly complex replicative systems. Chemistry of course routinely deals with problems of chemical reactivity in its broadest sense - how stuff reacts. But until relatively recently, chemical research had largely ignored the general class of replication reactions. And that's where systems chemistry comes in. By studying the chemistry of simple replicating systems - replicating molecules and the networks they establish - systems chemistry is beginning to fill the void separating chemistry from biology. To understand the workings of highly complex replicating systems - and that's what biology is - we first need to understand the workings of simple replicating systems.

So where is systems chemistry leading us? Through pioneering experimental work in this new area, the beginnings of some general rules that govern this class of materials are beginning to taking shape. Of course within the physicochemical world the central law that governs change is the Second Law of Thermodynamics. But as Schrödinger made so clear 70 years ago, the biological world is not explicable in Second Law terms. The Second Law offers no explanation for how the intricacy of even simplest life, say a bacterial cell, could have emerged from a stochastic chemical environment. So are there some as yet undiscovered laws of nature that may hold the secret to the life puzzle? Or, could it be that the key principles are all known, but the pieces of the puzzle haven't been put together in the right way?

We still do not know for sure. But an interesting possibility is coming together: that what makes the replication reaction so different to most other chemical reactions is that it is autocatalytic. Autocatalysis can open up the door to kinetic forces that are quite staggering. A molecule replicating just 79 times would become a mole, that's 6 x 1023 molecules. The kinetic power associated with exponential growth is able to create distinctly different chemical patterns, and within those patterns, I believe the key to the 'why life?' question can be found. For example, it is the exponential growth associated with some replicating systems that can lead not only to the establishment of persistent replicating entities, but also to the evolutionary process in which replicating systems undergo directed change - from poorer replicating systems to better ones. Evolution begins with chemistry.

More fundamentally, the replicating reaction and its potential autocatalytic character are leading us to reconsider the concept of 'stability'. Is stability just about energy, or does stability have a time/persistence aspect as well? Could the Second Law be viewed as a particular expression of a general Stability Law formulated in terms of persistence?

What is clear is that after a half century of considerable advances in our understanding of how biology operates, but little advance in our understanding of what biology is and how it connects with physics and chemistry, we are entering a new period. The biological and physical sciences are beginning to merge, as indeed they must, and through that merging, answers to the 'why life?' question may finally be within reach.

Many thanks to Piet Hut, Jim Cleaves and Greg Fournier for having organized that stimulating and thought-provoking event.