Emergent Properties

Emergent properties (e.g., disease, clinical observations) are difficult or impossible to predict. You don’t see heart pulse or skin pallor in your scanning tunneling microscope. Emergent properties typically have qualities not directly traceable to individual molecules. The whole is greater than the sum of its parts. These qualities are irreducible to the system's constituent parts. For example emergent properties in biology arise from the combination of individual atoms to form molecules such as amino acids, which in turn fold and refold to form proteins. These proteins assume their functional roles from their folds and interact to create even higher biological functions. So, for example, we can show that three molecules are found at certain concentrations only in diseased tissues, it’s very unlikely we’ll ever be able to show that changing these concentrations keep pre-diseased tissues from becoming diseased.

For a dramatic illustration of complexity of emergent behavior in biological systems see the study on changing just one gene in the simplest of organisms, the humble nematode worm.  Several years ago it was discovered that knocking out the daf-2 gene doubled the life expectancy of the nematode, ushering in optimism for a similar breakthrough in humans. Kim (2007) had the genius to isotope tag 1,685 proteins in both the daf-2 mutant and wild type worms, and to slice and dice them in a Cuisinart and measure the differences in abundance of each of these proteins. Of these 1,685 proteins, 47 had increased abundance and 39 had decreased abundance in the daf-2 mutants relative to the wild type worms. And these were proteins involved in amino acid biosynthesis, oxygen metabolism, mRNA translation and lipid transport – some pretty serious functions. One gene, albeit an important one, affected fully 5% of these measured proteins in the worm. It can be very difficult to uncover all the anastomoses around even a single molecular biomarker.

See Shapes of the Invisible (1997) for simply amazing examples of emergent properties in a variety of organic and inorganic materials.