Embry­on­ic stem cell research may offer rev­o­lu­tion­ary med­ical treat­ments because the embry­on­ic stem cell is the only cell we know of that can dif­fer­en­ti­ate itself into any oth­er type of cell, and can repli­cate itself indef­i­nite­ly. How­ev­er, embry­on­ic stem cell research is con­sid­ered con­tro­ver­sial because some con­sid­er that a blas­to­cyst (a fer­til­ized egg), from which embry­on­ic stem cells are obtained, is a human being.