--- title: "Fish schooling evolved about 60 times and vanished about 320 times; an AI study of 2,839 species" url: https://badiyaa.com/fish-schooling-evolution-cornell-2839-species/ published: 2026-11-11T14:21:00+00:00 modified: 2026-11-11T14:21:00+00:00 section: Science publisher: Badiyaa --- # Fish schooling evolved about 60 times and vanished about 320 times; an AI study of 2,839 species Fish schooling evolved about 60 times and was lost about 320 times over 350 million years, a Cornell-led study of 2,839 fish species found. Swimming in a school is not a one-way evolutionary street. A Cornell-led team reports that ray-finned fishes gained the habit of moving together about 60 separate times over the last 350 million years, and lost it about 320 times. The study, [published November 6 in the Proceedings of the National Academy of Sciences](https://news.cornell.edu/stories/2026/11/machine-learning-helps-explain-evolution-fish-schools), covers 2,839 species. That works out to more than five losses for every gain. Senior author Andrew Hein, an associate professor of computational biology, said experts would have guessed the opposite: “If you had asked me or other evolution of behavior experts before this study, we’d tell you that losses of collective behavior are probably very rare, but that’s simply not true.” ## How do you measure schooling in 2,839 species? Behavior is hard to score from museum jars, so the team leaned on machine learning. A text transformer, the same kind of model behind large language models, read written species descriptions and turned them into numbers that flagged whether a fish moves in groups. A second set of tools analyzed citizen science photos and videos, including images from iNaturalist, rebuilt the scenes in three dimensions and checked whether neighboring fish pointed the same way. The authors’ [earlier preprint](https://doi.org/10.64898/2026.04.06.716557) describes the sample as nearly 10% of all living ray-finned fishes, the most species-rich class of vertebrates. Earlier work on collective behavior had looked at one or two species per study, adding up to a few dozen in total, according to the university’s account. ## What the tree of fishes shows Schooling turned out to be rock-steady in some branches of the fish family tree and constantly switching on and off in others. Three patterns stood out. - Prey fish school more. Species lower in the food chain were more likely to move in groups, which fits the safety-in-numbers idea. - Diet matters. Group-living predators almost always eat prey that also travels in groups, supporting the idea that schooling helps fish find patchy food. - Schoolers diversify faster. Lineages in which every species schooled produced new species at a higher net rate than lineages that did not. First author Jay Love, a postdoctoral researcher in Hein’s lab, was careful about that last point: “We don’t know if the speciation rate is higher or the extinction rate is lower, but we know that through a combination of those two things, we have more species being generated.” ## Why give up the school? The researchers do not yet know why schooling vanished so often, but they list candidate costs. Groups can spread false alarms, when one jumpy fish bolts and the rest scatter. When food is scarce, sharing it with a crowd may not pay. And over long stretches of time, living packed together could raise the risk of shared disease. It is a useful counterweight to the idea that copying the crowd always helps, a theme that also runs through our piece on [mate choice copying in guppies, grouse and humans](https://badiyaa.com/mate-choice-copying-guppies-grouse-humans/). Fish habitat is a practical matter too, as when Kentucky [sank 1,700 used Christmas trees in Boltz Lake](https://badiyaa.com/kentucky-christmas-trees-boltz-lake-fish-habitat/). ## Limits The behavior scores come from machine reading of text and pictures rather than direct observation of every species, so some fish may be misclassified. The links with diet, predation and diversification are correlations across the tree, not experiments. Hein noted that the food-chain pattern is not “iron clad”: many prey species never school and many predators do. The preprint version reported “over 300 evolutionary transitions,” while the published figures from the university give about 60 gains and 320 losses; we use the published numbers. Co-authors came from Cornell, the University of Colorado Boulder and Florida Atlantic University, and the National Science Foundation funded the work. ## Further reading - [Cornell University: Machine learning helps explain evolution of fish schools](https://news.cornell.edu/stories/2026/11/machine-learning-helps-explain-evolution-fish-schools) - [Love et al. preprint: Collective behavior drives diversification across the tree of ray-finned fishes](https://doi.org/10.64898/2026.04.06.716557) *Image: Diego Delso, CC BY-SA 4.0 via Wikimedia Commons* *This article was produced with AI assistance and reviewed by our Editorial Desk. [How we work](https://badiyaa.com/editorial-policy/).*