ESPCI web site
Evolution is often seen as a blind process, driven by natural selection and random mutations. However, a study conducted by researchers [1] from ESPCI Paris - PSL and the Max Planck Institute challenges this perspective. Over three years, they tracked the evolution of a bacterial lineage, identifying and analyzing more than 500 mutations. Their research shows that natural selection not only favors beneficial mutations but can also shape genetic mechanisms to enhance an organism’s ability to evolve.
In this experiment, bacteria had to alternate between two phenotypic states to survive. Lineages unable to mutate efficiently disappeared, while those that adapted quickly took their place. An unexpected phenomenon emerged: a hyper-mutable locus—a specific region of the genome—evolved to facilitate these transitions. Through the duplication of a short DNA sequence, this locus experienced a mutation rate increase of 10,000-fold, resembling the "contingency loci" found in pathogenic bacteria.
This result is based on a key principle: in a fluctuating environment, lineages that are better at generating adaptive variation survive and spread. Over many generations, this dynamic shapes the relationship between genotype and phenotype. Beneficial mutations from the past become more accessible, making evolution appear less random than previously thought.
This study demonstrates how selection can embed evolutionary history into genetic architecture, optimizing the adaptability of lineages. Beyond bacteria, these findings shed light on how certain pathogens evade immune defenses and highlight a fundamental mechanism of evolution—one that, over time, refines its own processes.
Figure 1. Lineage Selection (A) Experimental protocol where a lineage alternates between CEL+ (yellow) and CEL– (blue) phenotypes through mutation. Each cycle starts with a single CEL+ genotype, followed by the selection of a CEL– mutant, and then a return to CEL+. Extinction occurs if the transition fails. (B) Schematic representation of competition among lineages in a meta-population, where only those capable of mutating between CEL+ and CEL– survive and become established.
–
Références :
Michael Barnett et al.,Experimental evolution of evolvability. Science 387, eadr2756(2025). DOI:10.1126/science.adr2756
Perspective, Enabling evolvability to evolve, A multilevel population architecture enables bacteria to evolve increased adaptability
Contact :
Scientific communication of ESPCI Paris - PSL : Paul Turpault - 