Why do all vertebraes have very similar forms during development?

All vertebrates exhibit similar forms during development due to shared evolutionary ancestry and the presence of conserved genetic pathways that govern early embryonic development. These common genetic mechanisms, such as the roles of Hox genes, regulate the body plan and segmentation, leading to similar patterns of growth and differentiation across species. Additionally, the fundamental processes of cell division, tissue formation, and organogenesis are largely conserved, resulting in analogous developmental stages among vertebrates. This similarity reflects the evolutionary principle of descent with modification, where basic body plans are retained while allowing for adaptations in different environments.