Since the advent of stem cell research, one barrier to furthering stem cell research has been religion. The destruction of an embryo that occurs when embryonic stem cells are extracted has angered and upset many religious groups, who see it as 'murder' or the destruction of human life. They do, however, tend to support the use of adult stem cells. With adult stem cells, extraction is from adult tissues and does not result in the destruction of an embryo. In this way, religious groups are pushing for a greater focus and research on adult stem cells.