Molecular biology of preimplantation embryos: primer for philosophical discussions

This article is based on a presentation at the First International Conference on Ethics, Science and Moral Philosophy of Assisted Human Reproduction. The goal is to provide scientific background for the discussion of philosophic issues. Recent advances in the systematic molecular analysis of preimplantation embryos are summarized, including the molecular identification of nearly all genes involved in preimplantation development and their detailed expression patterns. Notwithstanding a quantum leap in molecular understanding of preimplantation embryos, molecular evidence seems to provide no decisive definition of a threshold for the beginning of human life during preimplantation development.