Evolutionary biologists have finally discovered the oldest creature on Earth, who is also the closest living relative of the planet’s first animal. It is about the jellyfish combwho are also known as ctenophoresreports an article in the journal Nature.
These aquatic beings, possessing a nervous system, arose approximately a few years ago. 700 million years, long before the dinosaurs, who date back 230 million years. From then until now, these translucent and gelatinous animals have continued to inhabit the depths of the oceans.
Comb jellyfish or sponges?
The scientific debate over who was the longest-lived animal has long had two main contenders: comb jellies and sponges.
Sponges were believed to be more primitive than ctenophores, since, unlike them, they lacked neurons and muscles, complex characteristics commonly attributed to more developed animals.
However, in 2008, the story took a turn when scientists analyzed DNA fragments from both species and identified that the sponges possessed genes very similar to those of the ctenophores.
For that reason, they suggested that comb jellies would actually have branched before other aquatic creatures.
Since then, several studies have been published that support this theory, but they never showed conclusive evidence. Or, at least, that’s how it was until now.
oldest living animal
In his attempt to delve into the evolutionary trees of both animals, Daniel Rohsara biologist at the University of California (USA), devised a new method that explores the genomes of comb jellies, sponges and three other close single-celled relatives of early animals.
So, instead of comparing individual genes, as was done before, Rokhsar and his team looked at large-scale patterns in genomes, the set of genes on chromosomes, which evolve more slowly over time and whose changes are irreversible.
“As animals evolve, bits of DNA are exchanged, but the genes often stay on the same chromosome. However, occasionally, chromosomes fuse and mix, allowing genes to irreversibly move to a new chromosome.
The conclusion of this new study, published on May 17, was that the ancestor of the comb jellyfish was the first to diverge from the ancestor of all animals, making it our oldest living relative.
Casey Dunn, an evolutionary biologist at Yale University who was not involved in the research, argues that “understanding these deeper relationships in the animal tree of life” will help “reconstruct the history of the origin and evolution of many complex traits such as the nervous system and animal symmetry”.
With information from Science and Scientific American
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