As some researchers using a computational model claim, according to ScienceDaily:
Evolutionary theorist Stephen Jay Gould is famous for describing the evolution of humans and other conscious beings as a chance accident of history. If we could go back millions of years and “run the tape of life again,” he mused, evolution would follow a different path.
A study by University of Pennsylvania biologists now provides evidence Gould was correct, at the molecular level: Evolution is both unpredictable and irreversible. Using simulations of an evolving protein, they show that the genetic mutations that are accepted by evolution are typically dependent on mutations that came before, and the mutations that are accepted become increasingly difficult to reverse as time goes on.
The study focuses exclusively on the type of evolution known as purifying selection, which favors mutations that have no or only a small effect in a fixed environment. This is in contrast to adaptation, in which mutations are selected if they increase an organism’s fitness in a new environment. Purifying selection is by far the more common type of selection. More.
Although the media release says boo about it, doesn’t this mean that Darwinian natural selection, as usually described is a minor factor in evolution? “[a]daptation, in which mutations are selected if they increase an organism’s fitness in a new environment” sounds a lot like “natural selection acting on random mutation.”
Gould and Dawkins, recall, were famously at loggerheads, so some clarity about siding with Gould would be welcome. But maybe it’s not easy these days to be clear about that?
Also, is not the “irreversibility” thesis support for Dollo’s law (not accepted in many quarters today)?
See also: Remember Dollo’s Law?: Once a trait was lost through evolution, it could not be regained.
Well, no one told the life forms about it, and frogs, snapdragons, and snakes, among other, apparently broke it with impunity, so that the “law” is in the process of being retired.
Here’s the abstract:
The phenotypic effect of an allele at one genetic site may depend on alleles at other sites, a phenomenon known as epistasis. Epistasis can profoundly influence the process of evolution in populations and shape the patterns of protein divergence across species. Whereas epistasis between adaptive substitutions has been studied extensively, relatively little is known about epistasis under purifying selection. Here we use computational models of thermodynamic stability in a ligand-binding protein to explore the structure of epistasis in simulations of protein sequence evolution. Even though the predicted effects on stability of random mutations are almost completely additive, the mutations that fix under purifying selection are enriched for epistasis. In particular, the mutations that fix are contingent on previous substitutions: Although nearly neutral at their time of fixation, these mutations would be deleterious in the absence of preceding substitutions. Conversely, substitutions under purifying selection are subsequently entrenched by epistasis with later substitutions: They become increasingly deleterious to revert over time. Our results imply that, even under purifying selection, protein sequence evolution is often contingent on history and so it cannot be predicted by the phenotypic effects of mutations assayed in the ancestral background. (paywall) – Premal Shah, David M. McCandlish, and Joshua B. Plotkin. Contingency and entrenchment in protein evolution under purifying selection. PNAS, June 2015 DOI: 10.1073/pnas.1412933112
Follow UD News at Twitter!