Early family ties: No sponge in the human f...(duce phylogenetic relationships from gen...)

Aiming to resolve these controversies, a group of international scientists led by Herv Philippe (Universit de Montral, Canada), Gert Wrheide (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," explains Wrheide. "This proposition generated a lot of attention in the past. But our results clearly disagree with it." The analyses also revealed that ctenophores and cnidarians most likely belong to a common group. "This group, the "coelenterates", is most closely related to the bilaterians," explains Wrheide. "Our results support, after much controversy, a hypothesis that was already formulated back in 1848."

The investigation also provides new insights into the development of individual organ systems. "Both coelenterates and bilaterians already h
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