Causal emergence might explain how living systems can operate

Erwin Schrödinger’s 1944 book What Is Life? is better known today for its answer than its question. Famously, Schrödinger proposed the concept of a code-script encoded in an ‘aperiodic crystal’ that enables life to avoid the disordered fate seemingly demanded by the second law of thermodynamics. That script, the conventional story goes, turned out to be the genome sequence in an organism’s DNA.

But what puzzled Schrödinger about life was that ‘only in the co-operation of an enormously large number of atoms do statistical laws begin to operate and control the behaviour of these assemblies with an accuracy increasing as the number of atoms involved increases.’ How can organisms exhibit predictable and orderly structures and behaviours if they are based on physical and chemical laws that are statistical, such that one might expect any orderliness to be ‘perpetually disturbed and made inoperative by the unceasing heat motion of the atoms’?

Even if you buy the idea of a genome as a code-script, it doesn’t solve that problem. Schrödinger acknowledged as much, saying that some ‘new type of physical law’ was required that can generate ‘order from order’, producing large-scale regularity from the information in the chromosomal code-script without falling prey to the molecular disorder surely present in the warm, wet environment of the cell. He speculated that perhaps his aperiodic crystal was sufficiently solid and large to bear comparison with a cog in clockwork. But that’s not so. Not only does DNA thermally fluctuate as much as any molecule, but the smaller molecular parts it encodes – RNAs and proteins – are even more subject to the stochastic contingencies of their generation, diffusion, interaction and degradation. Concentrations and expression rates can fluctuate, for example, and many interactions are non-specific . There can be no clockwork in an environment as noisy as the cell.