Cave lions split from modern lions some 1.5 million years ago – far earlier than previous estimates – according to new research by scientists in Sweden and Cardiff.
In a new study, published in the journal Cell, genetic information taken from extinct cave lions demonstrates that the species represented a highly distinct evolutionary lineage, which separated from modern lions more than a million years ago.
The genetic material was taken from 12 cave lion specimens, dated at between approximately 17 thousand and over 100 thousand years old. These specimens were recovered from caves, eroded river banks and permafrost, including two exceptionally well-preserved cave lion cubs from Northern Siberia.
The results also show that the cave lion interbred with modern lions and that this history was tightly linked to past climatic changes.
The research analysed 12 genomes from cave lions, spanning the last 100,000 years, and compared these with 20 genomes from modern lions in Africa and southern Asia.
"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.
A comparison of the genomes shows that cave lions and modern lions formed clearly distinct groups, indicating long-term evolutionary separation. While earlier estimates have suggested a relatively recent divergence, the new analyses support a much deeper split that may extend back well over 1.5 million years.
The researchers also identified genetic differences that likely contributed to the distinctive biology of cave lions. They found mutations unique to cave lions that are predicted to impact protein function, along with an excess of genetic changes in genes linked to brain function, vision, growth, and circulatory development. These findings are consistent with evidence from fossils and cave art suggesting that cave lions differed from modern lions in size, behaviour, and ecological adaptation.
Despite this long period of separation, cave lions and modern lions did not evolve in complete isolation. The team identified multiple episodes of interbreeding between the two lineages across tens of thousands of years. Although the genetic contribution from modern lions was relatively small, these events were widespread and occurred at different points in time.
The timing of this interbreeding appears to be closely linked to past changes in global climate, the researchers say. They found that the level of modern lion ancestry in cave lion genomes increased during periods when ice sheets were most extensive. During these colder phases, cave lion populations likely expanded southward, bringing them into contact with modern lions in regions such as Central and Southwest Asia.
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.
Genetic evidence points to a recently extinct population of modern lions in Southwest Asia as the most likely source of this gene flow – the transfer of genetic information from one population to another. These lions appear to have served as a contact zone between the two lineages during colder periods.
At the same time, cave lion populations themselves were highly dynamic. The data reveal extensive genetic connectivity between cave lion populations across Eurasia, with ancestry spreading rapidly over large distances and becoming homogenised within relatively short time spans.
The research was completed at the Centre for Palaeogenetics, a joint initiative by Stockholm University and the Swedish Museum of Natural History. The research, Palaeogenomes reveal the evolutionary relationship between cave and modern lions , was published in Cell.
