ИСТИНА

During the last century the Haeckel's Gastraea theory remained a predominant concept of transition to multicellularity. According to this theory, the Metazoan ancestor was a blastula-like colony, which had subsequently undergone cell differentiation. However, recently accumulated evidence suggests that the Gastraea theory poorly accommodates extant unicellular relatives of Metazoa. It does not account for the fact that many of these organisms possess a complex life cycle, with different cell types coexisting at different stages. Moreover, some close Metazoan relatives from Ichthyosporea and Choanoflagellata develop multicellular assemblies that do not resemble the Haeckel's Blastaea. A survey of expanding genomic databases on these relatives reveals an unexpected abundance of genes involved in cell signalling and adhesion. Mapping major gene families and ecological traits onto the phylogeny indicates that presence of different cell types is not an intrinsic property of Metazoa. We here hypothesize an alternative view of the Metazoan origin.