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The novel aspect of this study is the construction of a data set of 1,719 genes that surpassed in size and quality the previous datasets used to treat phylogenetic kinship relationships between metazoan. The authors set out to use many more quality controls at all stages and proposed several methodological innovations to avoid a range of data errors resulting from contamination in high-throughput sequencing or potentials sequencing errors themselves, as well as gene duplications.

The origin of the nervous system and the muscles

Several studies supported a typology in which the ctenophores are the brother group of all other animals (including Porifera group sponges). On the other hand, other phylogenomic studies supported the alternative scenario in which sponges (Porifera) are the sister group of all other animals (including the ctenophores), a hypothesis consistent with a single origin of the intestine, nerve cells and of muscle cells.

The results of Simion et al. suggest that sponges (Porifera) and not the Ctenophores are the first lineage to separate from other animals, supporting the classic view of morphologists. Indeed, the phylogeny established by Simion et al. suggests that the muscles and the nervous system appeared later than what the phylogeny supporting the Ctenophores supports the basis of animals.

These results, which are much more consistent with models of the appearance of animals from unicellular plants, point out that methodological problems must be carefully addressed and resolved in order to address difficult phylogenetic issues.