Sources of evolutionary contingency: chance variation and genetic drift

Abstract

Contingency-theorists have gestured to a series of phenomena such as random mutations or rare Armageddon-like events as that which accounts for evolutionary contingency. These phenomena constitute a class, which may be aptly called the 'sources of contingency'. In this paper, I offer a probabilistic conception of what it is to be a source of contingency and then examine two major candidates: chance variation and genetic drift, both of which have historically been taken to be 'chancy' in a number of different senses. However, contra the gesturing of contingency-theorists, chance variation and genetic drift are not always strong sources of contingency, as they can be non-chancy (and hence, directional) in at least one sense that opposes evolutionary contingency. The probabilistic conception offered herein allows for sources of contingency to appropriately vary in strength. To this end, I import Shannon's information entropy as a statistical measure for systematically assessing the strength of a source of contingency, which is part and parcel of identifying sources of contingency. In brief, the higher the entropy, the greater the strength. This is also empirically significant because molecular, mutational, and replicative studies often contain sufficient frequency or probability data to allow for entropies to be calculated. In this way, contingency-theorists can evaluate the strength of a source of contingency in real-world cases. Moreover, the probabilistic conception also makes conceptual room for the converse of sources of contingency: 'sources of directionality', which ought to be recognised, as they can interact with genuine sources of contingency in undermining evolutionary contingency.

Contingency and convergence in the theory of evolution: Stephen Jay Gould vs. Simon Conway Morris

“…This paper analyzes arguments in favor of the contingent or convergent character of the historical path of life's evolution on Earth as they were presented by two figures: Stephen Jay Gould and Simon Conway Morris. The role of contingency (Wong 2020;Hopster 2017;Ramsey and Pence 2016;Ćirković 2014) and that of convergence (Currie 2012;Losos 2011;Harmon et al 2005;Futuyma 2010;Stayton 2015aStayton , 2015b in evolution has been discussed extensively in the literature. The way these factors were used to develop the contingency thesis as promoted by S. J. Gould (Blount, Lenski, and Losos 2018;McConwell 2019;Turner 2011;Dresow 2019;Beatty 2006aBeatty , 2006b) and the convergence thesis as promoted by S. Conway Morris, has also been researched.…”