planted in the uterus. Since many people regard the normal human blastocyst as morally deserving of protection, the challenge is to find methods of deriving hESCs that either leave the blastocyst intact and unharmed or avoid the use of normal blastocysts in the first place.
The paper explains the science behind the six approaches and describes the hurdles that must be overcome in making them useful in future stem cell research. Even though none of these options is free from scientific challenges or ethical and political problems, Green feels that we should support research now to develop them as a supplement tobut not a replacement for existing methods of hESC derivation.