What are human embryonic stem cells and how are they obtained?
Human embryonic stem cells are the cells from which all 200+ kinds of tissue in the human body originate. Typically, they are derived from human embryos—often those from fertility clinics who are left over from assisted reproduction attempts (e.g., in vitro fertilization). When stem cells are obtained from living human embryos, the harvesting of such cells necessitates destruction of the embryos.