A cell is the basic unit of life, and there are two main types of stem cells: embryonic and adult. Embryonic stem cells can become any type of tissue or organ, while adult stem cells are more limited. Scientists want to advance embryonic stem cell research for potential medical benefits, as these cells can renew themselves and adapt to their environment. However, this research is politically and ethically complex, with debates around when life begins and whether embryos should be destroyed. Former President Bush allowed only limited funding and research using previously created embryonic cell lines. Religious views also vary, with some believing life begins at conception and objecting to embryo destruction or manipulation.