Evolutionary Chance Mutation: A Defense of the Modern Synthesis’ Consensus View

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Montréal, 2910 Edouard Montpetit Blvd., Québec, H3T 1G7 Canada ✉ E-mail: [email protected] Received 24 May 2010; Revised 28 July 2010; Accepted 12 August 2010 KEYWORDS Biased chance ● Chance ● Darwin ● Directed mutation ● Lamarckism ● Modern Synthesis ● Mutator mechanism ● Random mutation 1. Introduction Biologists usually agree that all genetic mutations occur by “chance” or at “random”1 with respect to adaptation. The claim dates back to Darwin’s conception of “spontaneous,” “accidental” or “chance” variation (Darwin 1859, 1868; Darwin and Seward 1903). The Modern Synthesis later redefined Darwin’s idea as rooted in the phenomenon of genetic mutation following a long period of controversy over the “chance” vs “directed” character of variation. The main purpose of this paper is to defend the “chance” character of genetic mutations, which I claim is a Darwinian tenet and part of the Modern Synthesis’ consensus view, against recent challenges, especially those advanced by Jablonka and Lamb (1995, 2005). During the last thirty years, experimental research in molecular genetics, in particular on microorganisms, has shown that certain molecular mechanisms – the socalled “mutator mechanisms” – can regulate mutation rates (increasing or decreasing them) in response to certain selective forces. Because of this causal connection between mutation rates and selective substrates, Jablonka and Lamb, along with other biologists, historians and philosophers of biology (Shapiro 1999, 2005; Francesca Merlin§ Philos Theor Biol (2010) 2:e103 OPEN ACCESS - Freely Available at philosophyandtheoryinbiology.org One central tenet of the Modern Evolutionary Synthesis (1930s-1950s), and the consensus view among biologists until now, is that all genetic mutations occur by “chance” or at “random” with respect to adaptation. However, the discovery of some molecular mechanisms enhancing mutation rate in response to environmental conditions has given rise to discussions among biologists, historians and philosophers of biology about the “chance” vs “directed” character of mutations (1980s-2000s). In fact, some argue that mutations due to a particular kind of mutator mechanisms challenge the Modern Synthesis because they are produced when and where needed by the organisms concerned. This paper provides a defense of the Modern Synthesis’ consensus view about the chance nature of all genetic mutations by reacting to Jablonka and Lamb’s analysis of genetic mutations (2005) and the explicit Lamarckian flavor of their arguments. I argue that biologists can continue to talk about chance mutations according to what I call and define as the notion of “evolutionary chance,” which I claim is the Modern Synthesis’ consensus view and a reformulation of Darwin’s most influential idea of “chance” variation. Advances in molecular genetics are therefore significant but not revolutionary with respect to the Modern Synthesis’ paradigm. MERLIN, F. — EVOLUTIONARY CHANCE MUTATION 2 OPEN ACCESS - Freely Available at philosophyandtheoryinbiology.org Wright et al. 1999, 2000; Sternberg 2002; Keller 2000), have questioned the Modern Synthesis’ claim that all genetic mutations occur by “chance” or at “random.”