where do stem cells come from

studies on human embryonic stem cells arehighly controversial, and the current law says that embryos must be destroyed after14-days. but why 14-days? what’s so significant about the two week limit, and should we evenkeep using it? hi there my science buddies. julian here fordnews. human embryonic stem cells are one of the most legally and morally contentiousareas of study. on the one hand, stem cells, both adult and embryonic, are valuable forresearching a huge range of illnesses and diseases, from cancer to diabetes to alzheimer’s.on the other hand, many people believe that this benefit to medicine comes at the costof potential human lives. if you want a bit of background on the moral and medical controversysurrounding stem cells, you can check out

either of these videos on screen. originally, the 14-day limit comes from a1979 united states department of health, education, and welfare report. a committee of theologians,psychologists, and doctors came to a compromise: human embryonic stem cells could be studiedfor two weeks after fertilization, beyond which time the cells would have to be destroyed.but this limit was fairly arbitrary, as at the time, scientists could not keep embryosalive in vitro for more than a few days. a later report, organized in 1984 by britishexistential philosopher mary warnock, justified the two week limit. the report states thaton the 14th or 15th day, a faint line of cells appears on the embryo, called the “primitivestreak”. this, it was argued, is a moment

that signifies that the embryo has becomean individual being, as before this time the embryo could potentially split into twin organisms. one of the reasons this stage appealed tothose who objected on moral grounds, was that if an embryo could split into two people,then it could not yet be an individual person. the rule codified an easy to measure mark,coupled with an unambiguous time frame; making the question less about conception or “asoul”, while still allowing for a religious and moral compromise. additionally, a 2002 report from californiastated that less than half of all fertilized embryos, both in vitro and in vivo, ever reachthe primitive streak, meaning that most of

embryos used for research would have beenunlikely to make it to term anyway.. but recent advances have made it possiblefor scientists to keep embryos alive for longer than two weeks, by simulating womb-like conditions.with the potential for further research using stem cells, the question has been forced again:is the 14-day limit still valid? some scientists say no. arguing that theycould use the research in preventing miscarriages, infertility, and birth defects which theybelieve to be more important than a more or less arbitrary time limit. for example, in2014, researchers were able to cure “induced parkinson's disease” in rats neuroscientistsused human embryonic stem cells to create neurons that produce dopamine, which is missingin those who suffer from the disease. although

no human clinical trials have been done, theseearly results with animals have been very promising. that said, other researchers in bioethicshave pointed out that even an arbitrary limit is better than no limit at all. as more restrictionsare lifted, the very real question becomes “where is the limit on human experimentationin the pursuit of knowledge?”