In a controversial announcement earlier this month, scientists with the company Colossal Biosciences claimed they have brought back dire wolves from extinction using genetic engineering.
Dire wolves (Aenocyon dirus) lived in North America during the last ice age and died out around 12,500 years ago, but fossils have preserved enough of these predators’ DNA for researchers to partly reconstruct their genome.
The announcement drew criticism from paleogeneticists and other experts, who argued that the newly created animals — three snow-white pups named Romulus, Remus and Khaleesi — are only like dire wolves in appearance and so are not true dire wolves. To “resurrect” the dire wolf, Colossal scientists made 20 tweaks to 14 genes in a modern-day gray wolf (Canis lupus) genome, modifying characteristics like body size and hair color.
“Colossal has said that the gray wolf and dire wolf genomes are 99.5% identical, but that is still 12,235,000 individual differences,” Nic Lawrence, a paleogeneticist and associate professor at the University of Otago in New Zealand, told Vox. “So a gray wolf with 20 edits to 14 genes, even if these are key differences, is still very much a gray wolf.”
In addition to the tiny number of DNA changes, experts pointed out that dire wolves and gray wolves aren’t closely related in evolutionary terms. While the two species share many physical traits and the wolf-pack social structure, a seminal study published in 2021 in the journal Nature indicated that dire wolves aren’t technically wolves.
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According to the study, dire wolves branched off from modern wolf-like canids — a group that includes gray wolves, coyotes (Canis latrans), dholes (Cuon alpinus), African wild dogs (Lycaon pictus) and African jackals — roughly 5.7 million years ago.
So just how closely related are dire wolves and grey wolves — and what does the best available evidence tell us about the evolutionary relationship between these species?
A distant relationship
The latest peer-reviewed research suggests that dire wolves and gray wolves are only distantly related, Mairin Balisi, a paleontologist and curator at the Raymond M. Alf Museum of Paleontology in California, told Live Science in an email.
In the 2021 study, scientists found that dire wolves and gray wolves share a last common ancestor 5.7 million years ago during a period known as the late Miocene, said Balisi, who studies the evolution of mammalian carnivores but did not contribute to the 2021 study.
The analysis, which was based on DNA extracted from five dire wolf fossils, “showed that dire wolves diverged from the ancestor of not just gray wolves, of not just the group comprising [gray wolves and their closest relatives], but of all wolf-like canids including African jackals,” Balisi said. “This distant relationship justifies the genus name Aenocyon for dire wolves differing from the genus name Canis for most other wolf-like canids.”
The 2021 study revealed what was a decidedly blurry picture of canid evolution. “Previously scientists had interpreted dire and gray wolves to be sister species, or at least cousins through another extinct large wolf, Canis armbrusteri, because of strong similarity in their bones and teeth,” Balisi said. C. armbrusteri lived in North America during the last ice age and was likely an ancestor of dire wolves, according to the study.
Previous research also placed the split between dire wolves and gray wolves much later than the 2021 study, with dates ranging between 2 million years ago and 2.5 million years ago, Balisi said.
Unanswered questions
The 2021 study clarified some aspects of canid evolution, but many questions remain unanswered. For example, it’s still unclear which wolf-like canids are most closely related to dire wolves, Balisi said.
It’s entirely possible that dire wolves are more closely related to African jackals than gray wolves, she said, despite their physical appearance being closer to gray wolves, adding that “future analyses on more and/or higher-quality genomic data may shed more light on the fine-scale relationships among these canids.”
African jackals are divided into two species — the black-backed jackal (Canis mesomelas), native to eastern and southern Africa, and the side-striped jackal (Canis adustus), native to sub-Saharan and southern Africa. The 2021 study found that African jackals diverged from other wolf-like canids around 5.1 million years ago, forming their own branch on the evolutionary tree approximately 600,000 years after dire wolves formed theirs.
Fossils show that dire wolves were larger than modern-day gray wolves and had more robust jaws and teeth, which enabled them to take down larger prey. Current studies of canid evolution rely on these fossils to determine the relationships between species, but the record may have erased crucial information, Balisi said. “It is possible that other traits that don’t fossilize as readily also set apart dire wolves from gray wolves today,” she said.
There is also a question mark over whether dire wolves and gray wolves ever interbred. While it is possible that they did, the 2021 study found no evidence for gene flow between the two species, or between dire wolves and coyotes, Balisi said.
“Wolf-like canids do hybridize today — e.g., gray wolves and coyotes — so interbreeding between dire and gray wolves may have happened and just has yet to be detected,” Balisi said. But gray wolves and coyotes are much more closely related to each other than gray wolves and dire wolves, so it may be that the latter two have evolved bigger reproductive differences, she said.
Fresh findings
Following Colossal’s announcement, the company uploaded a paper to the preprint database bioRxiv with new (but not yet peer-reviewed) findings about the dire wolf’s evolutionary history.
The results, based on two fossils dating to 13,000 and 72,000 years ago, suggest that dire wolves descended from a lineage that was itself born from interbreeding between two lineages: a sister lineage to the one that produced modern-day South American canids (Cerdocyonina) and a sister lineage to the one that produced the African wild dog.
The research may shed light on how dire wolves evolved as a species, but it does not claim to rewrite the findings of the 2021 study. Overall, the new clues “may be a valid update to the literature,” so long as they hold up to peer review, Balisi said.
Regardless of whether peer review deems the study robust, the currently available evidence tells us that dire wolves and gray wolves are not closely related, which means that Romulus, Remus and Khaleesi are not dire wolves.
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