A new article in Science, “Combating Evolution to Fight Disease,” notes that the neo-Darwinian, or “modern” synthesis of “[t]raditional evolutionary biology began in the 1930s” and “predated knowledge that genes were made of DNA and of the structure of DNA and how it replicates.” The article then observes that key assumptions of the neo-Darwinian synthesis are now being overturned:

Among the cornerstone assumptions were that mutations are the sole drivers of evolution; mutations occur randomly, constantly, and gradually; and the transmission of genetic information is vertical from parent to offspring, rather than horizontal (infectious) between individuals and species (as is now apparent throughout the tree of life). But discoveries of molecular mechanisms are modifying these assumptions.

One of those now-overturned assumptions, which underlies virtually all of modern population genetics, “molecular clock” studies, as well as the highly criticized methods often used to infer natural selection in genes, is that mutations are random and occur at a constant, gradual rate:

Even the assumption that mutations are random, constant, and gradual has been revised on the basis of molecular mechanisms of mutagenesis. For example, in bacteria, responses to environmental stress can activate mutagenesis mechanisms that increase mutation rate, which can potentially increase the ability of a cell to evolve, specifically when it is poorly adapted to its environment (when stressed). Most of a 93-gene network that promotes mutagenesis in Escherichia coli is devoted to sensing stress and activating stress responses that direct the bacterium to mutate when stressed. Stress responses also up-regulate mutagenesis in yeast and human cancer cells and underlie mutations induced by antibiotics that cause resistance to those very drugs, and others.

Mutations are also nonrandom in genomic space — for example, forming hot spots at DNA double-strand breaks, as demonstrated in bacteria and suggested by local clusters of mutations in cancer genomes.

The authors conclude that by targeting biological mechanisms that are preprogrammed to allow organisms to experience higher mutation rates and “evolve” when under stress, we can help stop the evolution of antibiotic resistant microbes which are trying to evade antibiotics. It’s a fair point, even though antibiotic resistance entails trivial degrees of evolutionary change. Their conclusion, however, is telling:

The evolutionary biologist Theodosius Dobzhansky famously noted that “nothing in biology makes sense except in the light of evolution,” but perhaps, too, “nothing in evolution makes sense except in the light of biology.”

I agree with that statement wholeheartedly, as well as the authors’ point that molecular biologists need to pay more attention to the mechanisms of evolution when fighting disease. But given the toppled assumptions of the modern synthesis, I would add that evolutionary biologists need to pay more attention to molecular biology, which is overturning some central ideas that underlie modern evolutionary thinking. In fact, it seems that a lot of evolutionary claims no longer makes sense in the light of biology.

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