Support WBURAdvance In Human Embryo Research Rekindles Ethical DebatePlay04:38Download AudioRob SteinMay 04, 2016 ShareMolecular markers show structures and cell types within a human embryo, shown here 12 days after fertilization. The epiblast, for example, appears in green. (Gist Croft, Alessia Deglincerti, and Ali H. Brivanlou/The Rockefeller University)