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

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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
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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
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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.”