DNA of living animals contains all the information about their ancestors in the past
In the slow crawl of an Antarctic octopus lies a record older than human civilization: scientists have read the DNA of 96 Turquet's octopuses and found, written in their genes, the story of a catastrophic ice sheet collapse 125,000 years ago. When Earth's temperatures last resembled our own, the West Antarctic ice sheet melted entirely, briefly uniting populations of these seafloor creatures across seas now divided by ice. The discovery is not merely a chapter in natural history — it is a warning, encoded in living tissue, about what warming climates have done before and may do again.
- The West Antarctic ice sheet is already the largest driver of global sea level rise, and a full collapse could submerge coastlines and displace hundreds of millions of people worldwide.
- For years, geoscientists suspected the ice sheet had collapsed during the Last Interglacial but lacked definitive proof — each geological study arrived with caveats that left the question open.
- Researchers turned to an unlikely archive: the DNA of slow-crawling octopuses whose immobility makes them living records of ancient geography, their interbreeding patterns revealing when ice barriers once vanished.
- By sequencing 96 samples collected across decades, the team confirmed that three now-isolated octopus populations interbred around 125,000 years ago — a genetic fingerprint that only makes sense if the dividing ice had disappeared.
- The method cannot yet pinpoint exactly when or how fast the collapse unfolded, but scientists are already gathering new samples and scanning other Antarctic species for the next chapter of Earth's frozen memory.
Scientists have found an unlikely witness to ancient catastrophe: the Turquet's octopus, a small creature that crawls along the Antarctic seafloor. By sequencing DNA from 96 of these animals — gathered over decades from research institutions and fishing nets — researchers confirmed that the West Antarctic ice sheet collapsed during the Last Interglacial, roughly 125,000 years ago, when global temperatures resembled those of today. It is the first definitive genetic evidence of an event long suspected but never proven.
The logic is elegant. Octopuses are homebodies, unable to swim freely like krill, so each population breeds in isolation and develops a distinct genetic signature. Today, Turquet's octopuses in the Weddell, Amundsen, and Ross seas are separated by massive ice shelves. But the DNA analysis revealed that around 125,000 years ago, these populations interbred — meaning the ice dividing them had melted away. Lead author Sally Lau of James Cook University described it as reading a biological time capsule: the genes of living animals carry the history of their ancestors across millions of years.
The stakes are immediate. A complete collapse of the West Antarctic ice sheet would raise global sea levels by three to five meters, redrawing coastlines and displacing hundreds of millions of people. Knowing how the ice behaved the last time Earth was this warm is not academic — it is essential for projecting what comes next. Outside experts called the genomic approach pioneering, noting that it brings an entirely independent line of evidence to a question that geology alone could not settle.
The method has limits: it cannot yet reveal exactly when the collapse began or how long it lasted. But Lau and her team are already looking ahead, planning to apply the same approach to other poorly understood Antarctic regions and searching for new species that might hold further secrets of Earth's climate past. The octopus has opened a door.
Scientists have found an unlikely witness to a catastrophic event that unfolded 125,000 years ago: the Turquet's octopus, a small creature that crawls along the Antarctic seafloor. By sequencing the DNA of 96 of these octopuses collected over decades from institutions and fishing nets worldwide, researchers have confirmed that the West Antarctic ice sheet collapsed during the Last Interglacial—a period when global temperatures matched those of today—providing the first definitive genetic evidence of an event that geoscientists had long suspected but never proven.
The breakthrough hinges on a simple biological fact: octopuses are homebodies. Unlike fast-moving marine species such as krill, these animals can only crawl along the ocean floor, which means they stay within their local populations and breed among themselves. This immobility creates distinct genetic signatures for each population. Today, Turquet's octopuses in the Weddell, Amundsen, and Ross seas are separated by massive ice shelves and cannot intermingle. But the genetic analysis revealed something striking: around 125,000 years ago, these isolated populations were connected. They interbred. The only explanation that fits is that the ice sheet that had divided them had melted away.
Sally Lau, a postdoctoral researcher at James Cook University in Australia and the lead author of the study published in Science, described the approach as reading a biological time capsule. "DNA of living animals today contains all the information about their ancestors in the past," she said. The team sequenced samples dating back to the 1990s, but the genetic data they extracted reached back millions of years, creating what amounted to a detailed family tree. By analyzing whether different octopus populations had interbred and pinpointing when that interbreeding occurred, the researchers could infer the geological history of the region without ever drilling into ice or rock.
The implications are sobering. The West Antarctic ice sheet is currently the largest contributor to global sea level rise. If it were to collapse entirely—as it did during the Last Interglacial—global sea levels would rise between three and five meters. That kind of change would reshape coastlines worldwide and displace hundreds of millions of people. Understanding how the ice sheet behaved the last time Earth's temperature climbed to current levels is therefore not academic curiosity but urgent practical knowledge. Jan Strugnell, a professor at James Cook University who conceived the idea of using octopus genetics to investigate the ice sheet's history, noted that this historical understanding will help scientists refine their projections of future sea level rise in a warming world.
The choice of octopus was deliberate and clever. The researchers needed a species that was relatively immobile, whose biology was well-studied, and whose DNA mutation rate and generation time were understood well enough to allow accurate molecular dating. Turquet's octopus fit all these criteria. Previous studies of crustaceans and other marine mollusks had hinted at ice sheet collapse, but they lacked the resolution and sample size to distinguish between a sudden collapse and a gradual migration of animals around the ice sheet's edges. This study, with its 96 samples and advanced genetic analysis, provided that clarity for the first time.
Experts outside the research team called the work pioneering. Andrea Dutton and Robert DeConto, geoscientists at the University of Wisconsin-Madison and University of Massachusetts Amherst respectively, noted that while geological evidence had been mounting for years that the ice sheet collapsed during the Last Interglacial, each study came with caveats. Bringing an entirely independent data set—the genetic history of living octopuses—to bear on the question posed new possibilities and raised urgent ones: if the ice sheet collapsed when temperatures were like today's, will it collapse again?
Lau acknowledged that the genetic approach has limits. It cannot reveal exactly when the collapse occurred or how long the event took. But with fresh octopus samples and more advanced DNA techniques, those questions might be answerable in the future. She and her team are already looking beyond this study, hoping to apply the same genomic methods to other poorly understood regions of Antarctica. "We're constantly looking for new species to test these science questions," she said. The octopus has opened a door. What other creatures might hold the secrets of Earth's climate past?
Notable Quotes
DNA of living animals today contains all the information about their ancestors in the past, so it's like a time capsule— Sally Lau, lead researcher, James Cook University
Understanding how the WAIS was configured in the recent past when global temperatures were similar to today will help us improve future sea level rise projections— Jan Strugnell, James Cook University
The Hearth Conversation Another angle on the story
Why an octopus? Of all the animals in the Antarctic, why did you choose this one?
Because it doesn't move much. An octopus crawls along the seafloor—it's not like a fish that can swim hundreds of miles. That means populations stay separate, genetically distinct. When you see them mixing in the DNA, you know something dramatic happened to the geography.
And the ice sheet collapsing would have done that?
Exactly. The ice shelves that separate the populations would have melted. Suddenly there's a corridor of open seafloor where there was ice before. The octopuses can move through it, meet, breed. That genetic signal is unmistakable.
How far back can you read in the DNA?
We had samples from the 1990s, but the genetic information goes back millions of years. It's like having a family tree written in code. We can see when different branches last connected.
And you found they connected 125,000 years ago?
Yes. And that's the crucial part—that's during the Last Interglacial, when Earth was as warm as it is now. So we know the ice sheet can collapse under conditions like today's.
What does that mean for the future?
If it collapses again, sea levels rise three to five meters globally. That's not a small thing. Understanding how it behaved the last time temperatures were this high helps us predict what comes next.