Discussion Questions: Cell Differentiation

Why do you think the heart forms early in an embryo's development?
How would you explain the similarities among bird, mammal, and reptile embryos at the early stages of development?
What directs the sequence of events during embryonic development?
People could observe the development of an embryo before they had the tools to see cells and parts of cells such as DNA. How do you think they explained the development from embryo to organism?
How would the discovery of DNA and how DNA "works" have changed how scientists could research development?