Charles Darwin, the father of evolution used to term "living fossil" to describe species that never evolved. Limited competition with other animals lessened to need to go through evolution to survive.

The rare deep-sea fish called the coelacanth dwell in caves off the South African coast. Until a discovery of a freshly dead coelacanth in 1938, the species was thought to have become extinct about 70 million years ago.

The genome of the coelacanth remains unchanged in tens of millions of years, one of the few species to have remained the same. The fins of coelacanths look quite similar to the legs of backbone-having animals. This superclass is known as "tetrapods" and is comprised of frogs, lizards, birds and mammals.

"We found that the genes overall are evolving significantly slower than in every other fish and land vertebrate that we looked at. This is the first time that we've had a big enough gene set to really see that," a research scientist at the Broad Institute of MIT and Harvard in Massachusetts, Jessica Alfoldi said.

Since coelacanths live in a deep sea environment that doesn't change, the genes have a lower rate of mutation compared to other animals. There is no need for them to evolve quickly as other animals did, transitioning from sea to land.

"We often talk about how species have changed over time. But there are still a few places on Earth where organisms don't have to change, and this is one of them," co-author of the study, Kerstin Lindblad-Toh said. Lindbald-Toh is the scientific director of the Broad Institute's vertebrate genome biology group.