The organism becomes a Chinese nest of boxes of qualities, and there is now seen to be no necessity for explaining change as change…Biology can then proceed to its real task, that of discovering the determined, material sequence of qualities, in each step of which organism and environment are involved as warp and woof. –Christopher Caudwell (1936/1986)
My views are mutating. I’m beginning to think that when evolutionary biologists characterize the source of variation on which natural selection operates as ‘random’ it is an attempt to impose on biologies the syllogism underlying Darwin’s ingenuous contribution: 1) heritible variation, 2) with effects on reproductive success, 3) produces natural selection.
Mutations, however, are routinely gamma-distributed across a genetic sequence; that is their mutation rates vary across sites and do so in particular directions (e.g., by transitions or transversions) and in domain-specific ways.
Take hemagglutinin, the influenza glycoprotein, characterized by a hypervariable head resistant to antibody memory surrounding a conserved core used to key the virus into target cells. Ostensibly selection operates in favor of surface hypervariability at the level of the phenotype. But we might ask whether it does so in such a way that imprints upon the mutation process itself.
Perhaps we have here a generalization of directed mutagenesis, but more an epiphenomenon arising from the very fabric of biological reality, however stochastic its short-term rhythm.
The counterargument is that there are influenza quasispecies that originate expressing little variation in the hypervariable region and/or with lots of variation in the conserved region. They just don’t make it through the selection filter. They do not become part of the population of sequences that characterize the gamma distribution. Shades of Nassim Taleb on silent evidence.
But I think this misses the point or, better yet, maybe makes the point. Assuming the source of variation precedes selection and not also the other way around misses a causal interpenetration at the heart of our biologies. Selection can shape the stereochemical drama by which mutations arise.
That is, mutation–or recombination or reassortment–isn’t just a statistical event, emerging as a kind of Platonic orphan. It is also a bloody biochemical event embedded in the real-world push-and-pull of molecules forming and breaking and in the path-dependent evolutionary trajectories shaped by passing historical circumstance. Following the theme of our blog, such histories would include the agroecological regimes humanity imposes.