Washington, April 3 (ANI): A new research has rebuffed a theory which said that humans have descended from a sponge, and has determined that all sponges descended from a unique sponge ancestor, who in turn was not the ancestor of all other animals.
The most ancient animal groups (phyla) include the Porifera (sponges), Placozoa, Cnidaria, and Ctenophora (comb jellies).
The sponges are extremely simply built, and have no organs. The placozoans also have a very simple structure. They have a flat, disk-shaped body, and no organs either. Comb jellies, the ctenophores, are life forms that resemble jellyfish.
The true jellyfish, however, are part of the cnidarians, a phylum that also includes corals and sea anemones.
The exact relationships among these early animal groups are still controversial, as different research groups have often obtained conflicting results.
In particular, results from morphological studies, which look for structural similarities between different organisms, frequently contradict the results from molecular biological studies.
The latter explore the functions of genes, and deduce phylogenetic relationships from gene sequences.
Aiming to resolve these controversies, a group of international scientists led by Herve Philippe (Universite de Montreal, Canada), Gert Worheide (LMU Munich, Germany) and Michael Manuel (University of Paris, France) performed the most comprehensive study to date and investigated 128 genes from a total of 55 species - including nine poriferans, eight cnidarians, three ctenophores and the single known species of placozoans.
Their analyses were based on a relatively new approach called phylogenomics, which determines the evolutionary relationships of life forms by comparing large datasets of gene sequences.
Together with biochemists, evolutionary and computational biologists from Germany, France and Canada, the team analyzed more than 30,000 amino acid positions.
Using computer analyses, the researchers then estimated a phylogenetic tree that displays how related the studied animals are.
One of the most significant outcomes of this study is new evidence that all species of sponges are descendants of a single ancestor.
On the other hand, Bilateria, which include worms, mollusks, insects, and vertebrates, did not descend directly from this "spongy" ancestor.
"If the ancestral animal would have had a sponge-like organization or body, as some earlier molecular studies repeatedly claimed, then we would all be descendents of such sponge-like organisms," explained Worheide.
"This proposition generated a lot of attention in the past. But, our results clearly disagree with it," he added. (ANI)