Evolution and favored change: a principle of least selection

Abstract Favored biological characteristics can evolve by a subtle path, but beneficial selection has predictable qualities to guide thought. These favored pathways are paths of “least selection”. Faster evolution is least selection, more probable because earlier evolutionary success is simply, “success”. A more likely path also requires least selection in the form of least selected change. Truncation selections, accepting only extreme values of a distributed quantity, produce greater change in population means. Truncation selection therefore readily offers a least selection. Assuming selection for a Normally-distributed quality, truncation is enhanced via simple dependences on increased standard deviation and higher selection threshold (consistent with some population survival). Least selection applies to both chemical and biological evolution, and can be estimated in general form, without reference to its genetics, from an underlying phenotypic distribution. Chemical truncation selection is free of the Haldane cost of natural selection; potentially yielding very rapid early evolution. Notably, a principle of least selection unifies prior examples of quick evolution. For example: the ‘crescendo’ of accurate codes leading to the Standard Genetic Code facilitates a least selection. More generally, evolutionary extinctions and radiations are events with multiple coercive thresholds; thus Earth’s history offers many wide-ranging truncation/least selection events.