The Biggest Extinction Event in History and What Survived It — New Clues From Squid Genomes

New squid genome research reveals how these animals survived Earth's worst extinction. The clues have profound implications for understanding ocean life in a warming world.

The end-Permian extinction event of 252 million years ago is the reference point for catastrophic biological loss: 96 percent of marine species eliminated, 70 percent of terrestrial species gone, the food webs that had evolved over hundreds of millions of years collapsed and rebuilt from the survivors. Understanding what properties allowed specific lineages to survive while vastly more species perished is one of the most important questions in evolutionary biology — because those properties are precisely what will matter as human-caused climate change accelerates.

The squid and cuttlefish genome research published in April 2026 adds specific molecular detail to the survival story. The genome comparison across multiple cephalopod species — squids, octopuses, cuttlefish, and nautiluses, which span the survival and extinction categories in different ways — revealed specific gene families that are expanded in the lineages that survived the end-Permian and contracted or absent in those that did not.

The most consistent finding involves gene families associated with hypoxia tolerance — the ability to function with reduced oxygen levels. The end-Permian extinction involved dramatic ocean deoxygenation as warming surface temperatures disrupted the thermohaline circulation that delivers oxygenated water to depth. Marine animals that could tolerate reduced oxygen concentrations survived; those that required higher oxygen levels perished disproportionately.

Squid and cuttlefish carry multiple copies of hypoxia-response genes — the genomic legacy of selection pressure during exactly the kind of environmental stress that the Permian extinction produced. The genome analysis suggests this expansion was not random but reflects a sustained period of selection for hypoxia tolerance that the end-Permian event provided.

For current ocean biology: human-driven climate change is producing ocean deoxygenation — not at Permian speed, but at rates that are measurable and accelerating. The animals that will tolerate this change best are, the new research suggests, those with similar genomic architecture to the Permian survivors. Understanding which modern marine species carry that architecture is directly relevant to predicting which ocean ecosystems will be most resilient.