Fossils show different species of woolly mammoths were interbreeding, creating hybrids

Mammoths are among the most iconic Ice Age animals. In North America, two main species lived side by side: the woolly mammoth in colder northern regions, and the Columbian mammoth across warmer southern landscapes.

Scientists once thought these species remained separate, shaped by different climates and diets. But fresh evidence shows their story is much more intertwined.

Fossil teeth discovered in Canada reveal that these giants were not only neighbors but also partners.

Genetic studies confirm that Columbian and woolly mammoths interbred repeatedly, creating hybrids that carried traits of both lineages.

Understanding mammoths – the basics

Mammoths were large, hairy relatives of today’s elephants that roamed across North America, Europe, Asia, and Africa during the Ice Age.

They had long, curved tusks that could grow up to 15 feet and thick coats of hair to help them survive the cold, harsh climates.

Most mammoth species, like the woolly mammoth, thrived in grassland ecosystems where they grazed on grasses, shrubs, and small plants.

Their size and strength made them important “ecosystem engineers,” meaning they helped shape their environment – for example, by knocking down trees and spreading seeds as they moved.

Mammoths began to disappear about 10,000 years ago, with the last small populations surviving on Arctic islands until around 4,000 years ago.

Scientists believe that a combination of climate change and human hunting pushed them toward extinction.

Teeth reveal hybrid mammoths

Two molars found in western Canada provided the breakthrough. DNA analysis revealed that one animal carried over 21 percent Columbian ancestry, while another held nearly 35 percent.

The results show that hybridization happened many times over thousands of years, not just as isolated encounters.

“Traditionally, we’re taught that different species can’t breed together,” said study co-author Professor Adrian Lister.

“As our ability to investigate genetics has developed, however, we’re finding that this has actually happened many times.”

Mammoth DNA reveals early mixing

The research builds on earlier discoveries of even older DNA. A steppe mammoth tooth from Siberia revealed that Columbian mammoths originated through hybridization around 420,000 years ago.

That’s the same timeframe when wooly mammoths mixed with a distinct steppe lineage known as Krestovka.

The result was a species carrying DNA from both ancestors. As much as half of Columbian mammoth ancestry traces back to wooly mammoths.

What is striking now is that the gene flow did not stop there. Woolly mammoths also absorbed Columbian DNA, making their genetic history a two-way exchange.

Genetic diversity of hybrid mammoths

The two Canadian fossils studied by Dehasque and colleagues provide new depth. Radiocarbon dating places them at about 35,000 and 25,000 years old.

The younger specimen carried roughly 60 percent more Columbian ancestry than the older one. This means interbreeding was a long-term process, producing increasingly mixed populations over time.

Genomic data also showed these hybrids had higher genetic diversity than Siberian woolly mammoths from the same period.

Diversity often helps mammoth species adapt, suggesting that hybridization may have been an advantage in unpredictable Ice Age climates.

Mammoths preserved useful traits

Interestingly, the Canadian hybrids did not always display clear physical signs of mixing. One of the older teeth looked fully woolly in form, despite its Columbian ancestry.

This suggests that natural selection favored traits best suited to the animals’ environments.

In northern plains, grass-eating woolly-like teeth persisted, while southern hybrids retained Columbian-like molars adapted to broader diets.

“Instead, we found that their teeth are still very like those of woolly mammoths, which are well-adapted to eating grasses on cold, open plains,” Lister explained.

“As the hybrids live in a similar environment, there’s a pressure for them to keep their woolly mammoth-like teeth.”

Sex and gene flow

The study also suggests that interbreeding was not entirely balanced. Genetic evidence points to male Columbian mammoths breeding more often with female woolly mammoths.

This bias left a stronger Columbian imprint in woolly genomes while keeping mitochondrial DNA firmly within wooly lineages.

Such patterns help explain why hybrids sometimes looked morphologically woolly even while carrying substantial Columbian ancestry. It also highlights how sex-biased interactions shaped the direction of genetic exchange.

Lessons from Ice Age mixing

These findings emphasize that hybridization is not rare in evolution. Other Ice Age species beyond mammoths, including polar and brown bears, also interbred when climate shifts pushed populations together.

Far from being evolutionary dead ends, hybrids often carried greater adaptability and resilience. Studying such cases matters today.

Conservationists worry that modern species, like the Scottish wildcat, face risks from hybridization with close relatives.

Insights from mammoths can help predict outcomes when changing environments push species into new overlaps.

Mammoth hybrids and climate shifts

The Ice Age cycles of ice sheet expansion and retreat repeatedly reshaped animal ranges. For mammoths, these climate shifts opened corridors like the Bering Land Bridge and then cut them off again.

Each wave of expansion and isolation offered new opportunities for mixing.

“Understanding how species can mitigate environmental change is very important at the moment, and we can look to past climate change to help with that,” noted Lister.

Although mammoths ultimately vanished, their history reveals both the power and limits of hybridization as a survival strategy.

The study is published in the journal Biology Letters.

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