North American mammoths interbred far more often than previously believed, according to new research, which suggests that hybrids were surprisingly common in the past 400,000 years.
The new evidence was covered from fossilized teeth discovered in Canada displaying a mix of Columbian and woolly mammoth genes. The findings, published in Biology Letters, may prompt us to reconsider how evolution occurs, potentially carving out a larger role for hybridization in the process.
North America’s Mammoths
During the last Ice Age, two mammoth species dominated the North American continent, yet each held separate territory. Present-day Canada and northern portions of the United States were home to the woolly mammoth, while the Columbian mammoth reigned further south. Each species was uniquely adapted to the local climate and food supply prevalent in its respective geographic area. These adaptive differences led to the assumption that the species rarely intermingled and largely remained in the region to which they were acclimated.
But before those two great species came to roam the North American continent, scientists long believed that they evolved from a common ancestor on the other side of the globe. The suggested evolutionary model followed a linear progression, from one species to another, as the creatures migrated around the world. On the Eurasian landmass around 700,000 years ago, the woolly mammoth evolved from the steppe mammoth. Then, after the woolly mammoth crossed the now sunken land bridge connecting Siberia and Alaska, the species arrived in North America. From there, the species continued south, where it gradually adapted to a warmer climate and evolved into the Columbian mammoth.
Hybrid Genetics
Two mammoth molars discovered in western Canada tell an intriguing story that overturns those earlier assumptions. Genetic analysis confirmed a rare and unusual finding: that the teeth belonged to hybrids of the two species.
What made the discovery even more astounding was that it was not a singular anomaly. Columbian mammoths were native to the lower latitudes where the teeth were discovered, yet the later teeth showed an even higher percentage of out-of-place Columbian DNA. The older fossil dates to approximately 36,000 years ago and contains more than 21% Columbian DNA, while the younger one dates to around 25,000 years ago and shows an increase to 35% Columbian genetics.
This means that instead of an isolated incident of interbreeding, followed by the regular breeding between woolly mammoths in the north where the teeth were found, the species continued to mix over thousands of years. A closer examination of the chromosomes reveals that mating pairs primarily consisted of Colombian males breeding with woolly females. This long-term mixing resulted in the most genetically diverse mammoth population yet discovered.
Such genetic diversity can increase a species’ resilience, and suggests that it may have been a key to the long-term survival of America’s ancient mammoth population.
Rethinking Evolution
“Traditionally, we’re taught that different species can’t breed together,” co-author Professor Adrian Lister said. “As our ability to investigate genetics has developed, however, we’re finding that this has actually happened many times.”
Earlier evidence of mammoth hybridization was discovered on the other side of the globe in Krestovka, Siberia, in 2021. At that time, another mammoth tooth, dated to 1.2 million years ago, also displayed mixed genes. The DNA recovered from the Krestovka fossil, however, put a hole in the earlier linear evolution theory. Instead of a direct line of descent, the DNA suggests that one group of steppe and woolly mammoths bred to produce Columbian mammoths as a hybrid species.
Intriguingly, this mixing of species likely occurred in North America after both woolly and steppe mammoths arrived in the region.
Researchers already knew that interbreeding resulted in Columbian mammoths with up to half of their DNA coming from woolly mammoths. The surprise in this new study was finding the opposite occurring, where woolly mammoths were inheriting a higher amount of Columbian genes.
“The approach we’ve taken to investigate these mammoths could potentially be applied to other extinct animals as well,” Lister said. “By reconstructing their history, we’ll be better able to see the role that hybridisation has played in the evolution of the species we see today.”
The paper, “Genomic and Morphological Analysis Reveals Long-term mammoth hybridization in British Columbia, Canada,” appeared in Biology Letters on September 24, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.