For a long time, scientists assumed the extinct cave lion was basically just a bigger, tougher version of the lions we know today. Now, a study published in the journal Cell suggests that picture is completely wrong.
A team of researchers from Sweden and the UK analysed ancient DNA from cave lions and discovered they were a unique branch of the lion family tree, one that split off from modern lions more than a million years ago. The research also reveals a fascinating twist: cave lions and modern lions occasionally mingled, and climate change was the reason why.
A lineage all their own
The study was led by scientists at the Centre for Palaeogenetics in Stockholm, a joint initiative between Stockholm University and the Swedish Museum of Natural History, alongside colleagues in the UK. The team analysed 12 genomes from cave lions found across Eurasia and the northernmost parts of North America, covering more than 100,000 years of history. They compared these with 20 genomes from modern lions in Africa and southern Asia.
The cave lion DNA came from teeth, bones, and even soft tissue, including two remarkably well-preserved cubs found frozen in northern Siberia.
“Cave lions have often been portrayed as just a larger, more rugged version of modern lions,” says lead author David Stanton, a former postdoc in Stockholm and now a lecturer at Cardiff University. “But what we see in their genomes is something much more remarkable — a lineage that has been evolving independently for over a million years, accumulating its own unique biological features.”
Earlier studies had suggested cave lions and modern lions parted ways relatively recently. The new findings push that split much further back, possibly more than 1.5 million years ago.
Built differently
The researchers also found genetic clues to what made cave lions unique. They identified mutations that likely changed how certain proteins worked, plus an unusually high number of changes in genes linked to the brain, vision, growth, and circulation.
This fits with what fossils and ancient cave paintings have hinted at for years: cave lions weren’t just hefty versions of today’s lions. They looked, behaved, and lived differently, adapted to a colder and harsher world.
When climate brought them together
Despite being separated for over a million years, cave lions and modern lions weren’t completely cut off from each other. The DNA shows they occasionally interbred, not just once, but repeatedly across tens of thousands of years. The genetic input from modern lions was small, but it happened in many places and at many points in time.
The most surprising finding? These encounters seem to have been driven by climate. When the planet got colder and ice sheets expanded, cave lions likely moved south in search of better conditions. That pushed them into regions like Central and Southwest Asia, where modern lions were living and the two groups met.
“Our results suggest that past climate change did more than reshape habitats. It actively brought species together, creating brief opportunities for interbreeding that would not have existed otherwise,” says senior author Love Dalén, a professor and research group leader at the Centre for Palaeogenetics in Stockholm.
The genetic trail points to a now-extinct group of modern lions in Southwest Asia as the most likely meeting point, a kind of crossroads where the two lineages occasionally overlapped during the coldest periods.
A connected world
The study also shows cave lions themselves were remarkably mobile. Genetic links between populations stretched right across Eurasia, with ancestry spreading rapidly over huge distances in relatively short periods of time.
Far from being isolated giants of the Ice Age, cave lions were part of a dynamic, interconnected world — one shaped by movement, climate, and the occasional chance encounter with their distant cousins. It’s a reminder that even species we think of as long gone still have surprising stories to tell, locked away in their DNA.
Stanton D, Bergström A, Heintzman P et al. Paleogenomes reveal the evolutionary relationship between modern and cave lions. Cell, 2026; DOI: 10.1016/j.cell.2026.05.007