Stanley Shostak
The symbiogeny hypothesis (1) attributes the origin of stem-metazoans to the formation of symbiogens of eukaryotic epithelial-like spheres fused with ameba-like cells and (2) credits the intra-organismic evolution of metazoan tissues and differentiated cells to competition, interactions, and selection among hereditable variations originating in symbiogens. Data consistent with the symbiogeny hypothesis are drawn from the fossil record of Doushantuo phosphites, molecular phylogenetics, tissue segregation and flexibility, and from the epithelial to mesenchymal and mesenchymal to epithelial transformations during development and malignancy.