Embryonic stem cells
Embryonic stem cells are taken from the inner part of a young embryo, also known as a blastocyst. An embryo reaches the blastocyst stage about 4-5 days after fertilization. At that point they contain about 50-150 cells.
Embryonic stem cells can differentiate into the three "germ layers": ectoderm, endoderm and mesoderm. The 220 types of cells in humans are all based on these germ layers. Some scientists have shown effectively that embryonic stem cells have greater differentiation potential, and divide into greater numbers, than adult stem cells can.
Pro-life conservatives consider taking stem cells from human embryos as tantamount to abortion, which they believe to be a hideous and evil practice. In actual fact, embryos used for stem cell research are already condemned to death because most of them are the byproduct of In Vitro Fertilization procedures which generate many more embryos than are needed to implant in the woman. With no further use for these embryos, they are often destroyed. Embryonic stem cell research does not result in the destruction of any additional embryos. [1]
President Bush was pressured by Scientists into funding stem cell research[1].