Research on an ancient family of sharp-nosed fish known as gars has found the first convincing evidence that a biological mechanism may explain these fish’s “living fossil” status. Some living organisms have extraordinarily low species diversity and physical diversity from ancient ancestors; This led Darwin to coin the term in 1859. However, clear evidence for the mechanism of living fossils was not previously available.

“Our paper shows that living fossils are not just strange historical events, but a fundamental indicator of the evolutionary process in nature,” says Chase Brownstein, an evolutionary biologist at Yale University. “Not only does this help us better understand the planet’s biodiversity, but it could also potentially one day be applied to medical research and improving human health.”

Braunstein and colleagues from the US and China discovered two different species of long-nosed garters (Lepisosteus osseus) and alligator gars (Atractosteus spatula) – They can produce fertile hybrid offspring even though 105 million years have passed since their last common ancestor.

The last common ancestor of horses and donkeys was just 4 million years ago. Although they can mate successfully to produce offspring, known as mules, the hybrid is usually sterile. The team found that gars have the oldest known common ancestor of different species forming fertile hybrids, actually about 60 million years old.

Analysis of 1,105 DNA coding regions in 481 species of jawed vertebrates found that gars had the slowest rates of molecular evolution; This may explain why their hybrids, as separate species, may still be viable and fertile after 100 million years. When genetic change is slow enough that even very different species can interbreed and create hybrids, the evolution of new species can also slow down.

“We show that the slow rate of molecular evolution of sea urchins inhibits their rate of speciation,” says Thomas Neer, an ichthyologist at Yale University. “In fact, this is the first time science has shown that a lineage meets the criteria for a living fossil through a unique aspect of its biology.”

Sturgeon and paddlefish, common species known to produce fertile hybrids, have similarly slow evolutionary rates. But when it came to slowness, Gars was the clear winner.

Higher rates of evolution mean that normally isolated populations are less likely to be compatible with each other if they somehow come into contact and reproduce, the researchers say.

“The slower a species’ genome mutates, the more likely it is to interbreed with a single species from which it has been genetically isolated over a long period of time,” says Brownstein.

Researchers note that some living fossils, such as the tuatara, may be “an accident of history” (sphenodon punctatus) was one of the few living fossils that, unlike gars, did not have an extremely slow genome rate. They believe that the secret of living fossils produced by ultra-slow molecular evolution, such as pottery, is a powerful DNA repair mechanism that allows mutations to be corrected.

“Most cancers are somatic mutations that represent failures in the individual’s DNA repair mechanisms,” Neer says. “If further studies prove that gar’s DNA repair mechanisms are highly efficient and we discover what makes them so, we can begin to think about potential applications in human health.”