Evolution leaves behind the 'living fossil' coelacanth fish
One of the few species to have hardly changed in tens of millions of
A deep-sea fish which became known as a "living fossil" has not
changed in appearance since before the time of the dinosaurs with the
help of an extraordinary genome that is barely evolving, a study has
The coelacanth, which lives in deep-sea caves off the coast of
Africa, was once known only from its fossils and so was thought to have
gone extinct at least 70 million years ago until a recently-dead
specimen was discovered by South African fishermen in 1938.
It is one of the few species to have hardly changed in tens of
millions of years and now scientists believe this physical stability is
mirrored in the coelacanth's genome - the threebillion "letters" of its
"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,"
said Jessica Alföldi, a research scientist at the Broad Institute of MIT
and Harvard in Massachusetts.
Charles Darwin first coined the term "living fossil" to describe
species that have endured unchanged due to limited competition with
However, Dr Alfoldi said that the description is not always helpful
because it suggests a relic from the past that has been brought back to
life. "It's not a living fossil; it's a living organism.
It doesn't live in a time bubble; it lives in our world, which is why
it's so fascinating to find out that its genes are evolving more slowly
than ours," she said. Coelacanths grow about four feet long and have
conspicuously fleshy fins that resemble the limbs of four-legged land
animals with backbones, the vertebrate "tetrapods" such as frogs,
lizards and mammals. This and their ancient lineage suggested they may
be closely related to the first fish that made the evolutionary
transition from sea to land.
Scientists have speculated as to whether the unchanging physical
appearance of the coelacanth was truly because it was evolving slowly,
or whether its DNA was somehow evolving just as rapidly as other
The complete coelacanth genome shows that the genes do indeed match
the fish's appearance in terms of slower evolution, the researchers say
in a study published in the journal Nature .
The genes of the coelacanth have a lower rate of "substitution" - a
type of mutation - than other animals with backbones, which may reflect
the fact that they do not need to evolve quickly because they live in
the relatively unchanging environment of deep-sea caves where there are
few predators, the researchers say.
"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," said Kerstin Lindblad-Toh, scientific director
of the Broad Institute's vertebrate genome biology group, a co-author of
the study. "Coelacanths are likely very specialised to such a specific,
non-changing, extreme environment - it is ideally suited to the deep sea
just the way it is," Dr Lindblad-Toh said A genome analysis also found
that the coelacanth is unlikely to be directly descended from the first
fish to walk on land. A more likely candidate is the lungfish, which are
closely related but have a much more complicated genome, the scientists
- The Independent