Researchers’ quest to discover the “first” animal – the ancestor of all other animals – has taken a new turn.
A new study says that the hairdressers is more likely to be the first ancestor of animals, displacing an existing theory that the sponges they are the oldest in the world.
700 million years ago, when there were no rings of Saturn, sharks and trees, there may have been transparent swimming invertebrates known as ctenophores, says the study published in Nature.
“The most recent common ancestor of all animals probably lived 600 or 700 million years ago,” says Professor Daniel Rokhsar, a cell biologist at the University of California, Berkeley.
“It’s hard to know what they looked like because they were molluscs and left no direct fossil record, but we can use comparisons between living animals to learn about our common ancestors.
“It is exciting. We are looking back deep in time, where we have no hope of finding fossils, but by comparing genomes, we are learning things about these very early ancestors.”
The two contenders for the oldest animal are combs and an equally primitive species – sponges. Unfortunately, because these two species diverged genetically so long ago, it’s hard to pick a clear favorite.
“The results of sophisticated sequencing-based studies have been fundamentally divided,” said Rokhsar.
“Some researchers did well-designed analyzes and found that sponges branched off first. Others did equally complex and reasoned studies and took the packers. There hasn’t really been convergence on a definitive answer.”
The researchers looked at the chromosome evolution of sponges, scallops and a range of single-celled non-animals.
“Traditionally, sponges are widely considered to be the first surviving branch of the animal tree, because sponges have no nervous system, no muscles, and look a bit like colonial versions of some single-celled protozoa,” says Rokhsar.
“And so, it was a nice story: First came the single-celled protozoa, and then sponge-like multicellular consortia of such cells evolved and became the ancestor of all of today’s animal diversity.”
Instead, however, they found that comb jellies, genetically, looked distinctly more non-animal than animal.
“That was the proof – we found a handful of rearrangements shared by sponges and non-carnivores. In contrast, the beasts resembled the non-animals. “The simplest explanation is that cetaceans branched off before the rearrangements appeared,” said Rokhsar. So, while this likely won’t be the last we hear of the matter, this provides some compelling evidence that in the battle of the ancients, the crustaceans came first.
