At least not in their study of laboratory yeast. From ScienceDaily:
According to the existing theory, the “fittest” DNA would be that which showed up most frequently in subsequent generations. However, the scientists observed “fluctuations” that the theories could not account for.
“Mutations and genotypes that seem to have fallen behind can leapfrog and dominate,” said Cvijović.
What that means, she says, will be the subject of future research. However, it implies that evolution is, indeed, even more complex than previously thought.
“Our experiment suggests there may be a wide range of a large number of strongly beneficial mutations,” she said. “And their benefits are both very strong and very different from one another.” Paper. (paywall) – Alex N. Nguyen Ba, Ivana Cvijović, José I. Rojas Echenique, Katherine R. Lawrence, Artur Rego-Costa, Xianan Liu, Sasha F. Levy, Michael M. Desai. High-resolution lineage tracking reveals travelling wave of adaptation in laboratory yeast. Nature, 2019; DOI: 10.1038/s41586-019-1749-3 More.
From the Abstract: “We show that clonal competition creates a dynamical ‘rich-get-richer’ effect: fitness advantages that are acquired early in evolution drive clonal expansions, which increase the chances of acquiring future mutations. However, less-fit lineages also routinely leapfrog over strains of higher fitness. Our results demonstrate that this combination of factors, which is not accounted for in existing models of evolutionary dynamics, is critical in determining the rate, predictability and molecular basis of adaptation.”
If Darwinism mattered the way it used to, this would be heresy.
See also: Natural selection: Could it be the single greatest idea ever invented?