Following are similarities in the structures of embryos of all vertebrates:- In the embryonic stages, they all possess the ventral heart, aortic arches, gills and gill slits which are exactly like those of the fish embryo.  Presence of tail at some stage of development.  This shows that the animals are similar in origin and that they develop similarly, implying that they are related, have common ancestors. These observations support the idea of organic evolution i.e. these organisms started out as the same, gradually evolving different traits, but the basic plan for a creature's beginning remains the same. This similarity of basic plan is because of shared genetic material and those genes that are still the same among organisms.