Metazoan embryos around the gastrulation or an equivalent developmental phase exhibit distinct morphologies and associated overall tissue rearrangement dynamics. Yet, during this event they universally specify at least a primary body axis, demarcated by conserved expression of posterior (or oral in cnidarians) patterning determinants. Among them are T-box and Wnt genes, localized transcriptional activity of which is highlighted in blue. Note that marker gene expression patterns in the human embryo are speculative. Research efforts have shown that ESC or ESC-like populations from species across the animal kingdom can be (re-)aggregated in vitro and, although lacking the respective external environment and associated developmental cues, remain capable of recapitulating at least a basic transcriptional body plan with an anteroposterior (AP) and oral-aboral (OA) axis, respectively. Strikingly, comparison of examples of such in vivo or ex vivo systems highlights a remarkable overall similarity despite the varying geometry of the respective native embryo. This may point toward the existence of a conserved developmental mode that cells exhibit when released from their species-specific extraembryonic environment.