What is it about?
We compared thousands of genes across 86 species of jellyfish and their relatives to ask how often natural selection appears to have produced the same changes in proteins in different lineages. These repeated changes were surprisingly widespread. They were somewhat less common in more distantly related species, but remained more frequent than expected by chance even in lineages that separated more than 600 million years ago. Yet pairs of species that had independently evolved the same conspicuous traits—eyes, loss of the jellyfish stage, or upright colonies—did not share more repeated protein changes than other pairs. Instead, the changes were concentrated in genes involved in metabolism, immunity, and processing foreign chemicals. These results suggest that evolution often repeats at the molecular level, but this repetition reflects complex interactions between organisms and their environments rather than being tightly linked to the same obvious traits.
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Why is it important?
Repeated genetic changes are often treated as evidence that evolution follows predictable paths, especially when distantly related species have independently evolved the same trait. Our study shows why that inference requires caution. By searching genome-wide without first restricting the analysis to species that shared a particular trait, we found that adaptive molecular convergence was pervasive—even between lineages separated by more than 600 million years—but was not elevated among species that shared eyes, loss of the jellyfish stage, or upright colonies. Thus, a repeated genetic change cannot automatically be attributed to the most conspicuous trait two species share. It may instead reflect many less obvious interactions with their environments. Recognizing this widespread background of molecular convergence should improve how researchers identify the genetic basis of adaptation and help us judge how predictable evolution truly is.
Perspectives
This project began with a question about eyes: When eyes evolve independently, how often does evolution reuse the same genetic changes? To answer it, we mounted an expedition with an international team of students to collect diverse jellyfish and their relatives. Using those samples, we reconstructed both their relationships and the timing of their evolutionary history. We were astonished to discover that repeated genetic changes were extremely common whether or not the species we compared had eyes, and even between lineages separated by hundreds of millions of years. The project therefore led us far beyond our original question. It changed how I think about molecular convergence: its causes are probably much more varied and widespread than many evolutionary biologists have assumed.
Todd Oakley
University of California Santa Barbara
Read the Original
This page is a summary of: Adaptive molecular convergence is pervasive across deep time and largely decoupled from phenotypic convergence, Proceedings of the National Academy of Sciences, July 2026, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2616248123.
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