A Yahoo! News article offers the sensationalist headline, “An Incredible Organism is Evolving at Lightning Speed – Faster Than We Ever Imagined Possible.” (See Denyse O’Leary’s earlier commentary.) The body of the article itself provides a good summary of the original paper.¹ Unfortunately, neither the substance of the paper, nor the popular press summary, support the hyped header. The study identified variation in traits in this tiny crustacean. However, no complex new traits evolved and there was no net evolution.

As stated in the article linked above, “The study showed that the organisms experienced changing selection pressures, but that they all eventually cancelled out, meaning no dominant trait took over and influenced the organism’s evolution.” A press release from the authors at Arizona State University likewise notes that “The multiyear, genome-wide analysis of nearly 1,000 genetic samples from a Daphnia pulex population shows that most genetic sites experience varying selection, with an average effect close to zero, indicating little consistent selection pressure over different times and selection spread across many genomic regions.” (Emphasis added.)

A Little Rich

The paper itself notes,

The genome sequences of >800 isolates provide insights into patterns of selection that cannot be obtained from long-term molecular evolution studies, including the following: the pervasiveness of near quasi-neutrality across the genome (mean net selection coefficients near zero, but with significant temporal variance about the mean, and little evidence of positive covariance of selection across time intervals); the preponderance of weak positive selection operating on minor alleles; and a genome-wide distribution of numerous small linkage islands of observable selection influencing levels of nucleotide diversity. These results suggest that interannual fluctuating selection is a major determinant of standing levels of variation in natural populations, challenge the conventional paradigm for interpreting patterns of nucleotide diversity and divergence, and motivate the need for the further development of theoretical expressions for the interpretation of population-genomic data.

In view of these statements, it seems a little rich for the Yahoo! News editors to title their story, “An Incredible Organism is Evolving at Lightning Speed — Faster Than We Ever Imagined Possible.” If this is a prime example of the transformative power of evolution, the evidence is not at all impressive.

Notes

1. Lynch M, Wei W, Ye Z, Pfrender M. The genome-wide signature of short-term temporal selection. Proc Natl Acad Sci U S A. 2024 Jul 9;121(28):e2307107121. doi: 10.1073/pnas.2307107121. Epub 2024 Jul 3. PMID: 38959040; PMCID: PMC11252749.