Contemporary Status of Mutationism
With the arrival of molecular biology, scientists studying "molecular evolution" began to suggest mutational explanations for patterns such as genomic nucleotide composition, and eventually it became a characteristic of the field of molecular evolution to emphasize the role of mutation in evolution. Contemporary interest in mutationism is revealed by articles in mainstream research journals that advocate mutationist ideas, referring to Goldschmidt's concept of the Hopeful Monster, or using the label "mutationism" or "neo-mutationism". Phrases such as "new mutations" or "mutation-driven evolution" also indicate a departure from the "shifting gene frequencies" view of the Modern Synthesis, in which evolution consists of establishing a new multi-locus equilibrium for the frequencies of pre-existing alleles, without new mutations.
These contemporary writings suggest that mutation plays a role in evolution that was proposed by the "mutationists" but rejected in the Modern Synthesis. A key aspect of this role, advocated forcefully in mainstream journals, is "how single mutations can have huge effects that drive evolution", a result that is difficult to argue from retrospective analyses, but that appears clearly in laboratory evolution experiments, such as those of Lenski and colleagues (cited in ). According to Takahata,
"Unlike neo-Darwinism, which regards mutation as merely raw material and natural selection as the creative power, Nei's mutationism assumes that the most fundamental process for adaptive evolution is the production of functionally more efficient genotypes by mutation (especially birth and death of duplicated genes) and by recombination."
Another aspect of this role, discussion of which is restricted largely to trade journals in molecular evolution and genomics, is that patterns of diversity and rates of change reflect systematic biases in mutation. Stoltzfus and Yampolsky list examples in which mutation-biased evolution is either a plausible hypothesis or the received view. A case that has received much attention is in regard to genomic GC-content and the origin of isochore. The mutational hypothesis is that systematic differences in GC content emerge slowly due to the cumulative effect of mutational biases favoring GC or AT. However, because the bond is stronger and more resilient between the G:C pairs than between A:T pairs, a commonly proposed selective explanation is that a high GC-content is an adaption to harsh conditions, either high temperature or UV radiation. Both hypotheses were later disproved.
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